Some devices, such as the Raspberry Pi3, have a fixed offset between memory
addresses as seen by the host and as seen by the other bus masters. So add
a new PCD that allows this fixed offset to be recorded, and to be used when
returning device addresses from the DmaLib mapping routines.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
In preparation of adding support to ArmDmalib for DMA bus masters whose
view of memory is offset by a constant compared to the CPU's view, clean
up some abuse of the device address.
The device address is not defined in terms of the CPU's address space,
and so it should not be used in CopyMem () or cache maintenance operations
that require a valid mapping. This not only applies to the above use case,
but also to the DebugUncachedMemoryAllocationLib that unmaps the
primary, cached mapping of an allocation, and returns a host address
which is an uncached alias offset by a constant.
Since we should never access the device address from the CPU, there is
no need to record it in the MAPINFO struct. Instead, record the buffer
address in case of double buffering, since we do need to copy the contents
(in case of a bus master write) and free the buffer (in all cases) when
DmaUnmap() is called.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
If double buffering is not required in DmaMap(), the returned device
address is passed through ConvertToPhysicalAddress () to convert the
host address (which in case of DebugUncachedMemoryAllocationLib is not
1:1 mapped) to a physical address, which is what a device would expect
to be able to perform DMA.
By the same reasoning, a double buffer allocated using DmaAllocateBuffer ()
should be converted in the same way, considering that the buffer is allocated
using UncachedAllocatePages (), to which the above equally applies.
So add the missing ConvertToPhysicalAddress () invocation.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Instead of depending on ArmLib to retrieve the CWG directly, use
the DMA buffer alignment exposed by the CPU arch protocol. This
removes our dependency on ArmLib, which makes the library a bit
more architecture independent.
While we're in there, rename gCpu to mCpu to better reflect its
local scope, and reflow some lines that we're modifying anyway.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Translation table walks are always cache coherent on ARMv8-A, so cache
maintenance on page tables is never needed. Since there is a risk of
loss of coherency when using mismatched attributes, and given that memory
is mapped cacheable except for extraordinary cases (such as non-coherent
DMA), restrict the page table walker to performing cacheable accesses to
the translation tables.
For DEBUG builds, retain some of the logic so that we can double check
that the memory holding the root translation table is indeed located in
memory that is mapped cacheable.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The LinuxLoader application boots Linux in a way that prevents the OS
from accessing UEFI runtime services. Since we have better ways now
of invoking the kernel (via GRUB, or directly via the kernel's UEFI
stub), remove the obsolete LinuxLoader so that people will no longer
mistake it for a suitable reference of how to invoke the OS from UEFI.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Ryan Harkin <ryan.harkin@linaro.org>
The DmaBufferAlignment currently defaults to 4, which is dangerously
small and may result in lost data on platforms that perform non-coherent
DMA. So instead, take the CWG value from the cache info registers.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
This is ancient cruft that is no longer used, so remove it.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The GCC ARM builds have access to ADRL/LDRL macros that emit relative
symbol references, i.e., references that do not require fixing up at
load time (or FV generation time for XIP modules)
Implement equivalent functionality for RVCT: note that this does not
use movw/movt pairs, but the more compatible add/add/add or add/add/ldr
sequences (which Clang does not support, unfortunately, hence the use
of movw/movt for the GCC toolchain family)
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Define DISABLE_NEW_DEPRECATED_INTERFACES on the compiler command line by
default, to prevent deprecated interfaces from being used in core EDK2
code.
Bug: https://bugzilla.tianocore.org/show_bug.cgi?id=164
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Drop the include of AsmMacroIoLib.h, which contains GCC preprocessor macros
that RVCT does not use or require, given it has its own AsmMacroIoLib.inc
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
ArmPkg.dsc was a bit out of date, and some modules added over the past
years had not been added to its [Components] section yet.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ryan Harkin <ryan.harkin@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
This missing dependency has gone unnoticed until now, but it is breaking
the Omap35xxPkg.dsc build.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
AsciiStrCat() is deprecated / disabled under the
DISABLE_NEW_DEPRECATED_INTERFACES feature test macro.
The caller of CpsrString() is required to pass in "ReturnStr" with 32
CHAR8 elements. (DefaultExceptionHandler() complies with this.) "Str" is
used to build "ReturnStr" gradually. Just before calling AsciiStrCat(),
"Str" points to the then-terminating NUL character in "ReturnStr".
The difference (Str - ReturnStr) gives the number of non-NUL characters
we've written thus far, hence (32 - (Str - ReturnStr)) yields the number
of remaining bytes in ReturnStr, including the ultimately terminating NUL
character.
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael Zimmermann <sigmaepsilon92@gmail.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=164
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=165
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
AsciiStrCat() is deprecated / disabled under the
DISABLE_NEW_DEPRECATED_INTERFACES feature test macro.
The "Str" variable serves no particular purpose in the MRegList() and
ThumbMRegList() functions; replace it with the pointed-to "mMregListStr" /
"mThumbMregListStr" global variable (as appropriate), so that the new
AsciiStrCatS() calls are as clear as possible.
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael Zimmermann <sigmaepsilon92@gmail.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=164
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=165
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
All users have moved to the generic or accelerated versions in MdePkg,
so remove the obsolete BaseMemoryLibStm.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
During Mmu initialization in the CpuDxe, for a page table any bits set
in the 'NextSectionAttributes' are garbage and were set from bits that
are actually part of the pagetable address. We clear it out to zero
so that the SyncCacheConfigPage will use the page attributes instead
of trying to convert the (bogus) section attributes into page
attributes.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Kurt Kennett <kurt.kennett@microsoft.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Without an explicit .align directive, the Clang assembler defaults to
no alignment, which may result in instructions appearing misaligned in
the final executable. So use word alignment in all cases.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
As reported by Eugene, the practice of sizing the address space in the
virtual memory system based on the maximum address in the table passed
to ArmConfigureMmu() is problematic, since it fails to take into account
the fact that the GCD memory space may be extended at a later time, both
for memory and for MMIO. So instead, choose the VA size identical to the
GCD memory map size, which is based on PcdPrePiCpuMemorySize on ARM
systems.
Reported-by: Eugene Cohen <eugene@hp.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Eugene Cohen <eugene@hp.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Currently, we allocate a full page for the root translation table, even
if the configured translation only requires two entries (16 bytes) for
the root level, which happens to be the case for a 40 bit VA. Likewise,
for a 36-bit VA space, the root table only needs 16 entries of 8 bytes
each, adding up to 128 bytes.
So switch to a pool allocation for the root table if we can, but take into
account that the architecture requires it to be naturally aligned to its
size, i.e., a 64 byte table requires 64 byte alignment, whereas pool
allocations in general are only guaranteed to be aligned to 8 bytes.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
In commit 7d189f99d8 ("ArmPkg/Mmu: Fix bug of aligning new allocated
page table"), we fixed a flaw in the logic regarding alignment of newly
allocated translation table pages. However, we all failed to spot that
aligning page based allocations to page size is rather pointless to
begin with, so simply allocate a single page each time we add new pages
to the translation tables.
Also, drop the unnecessary cast.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The relations between T0SZ, the number of translation levels and the
size/alignment of the root table can be expressed in simple arithmetic
expressions, so get rid of the lookup table.
Note that this disregards the fact that the maximum value of T0SZ is
39 not 42 (as one would expect for the smallest VA size using 2 levels)
but since this corresponds to a VA size of 32 MB and 4 MB, respectively,
neither of which are sufficient to run UEFI, we can safely ignore the
distinction.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The ArmGicLib API function GicGetCpuRedistributorBase () declares
GicCpuRedistributorBase to iterate over the redistributors of all
CPUs, but then inadvertently advances GicRedistributorBase instead.
Reported-by: "Oliyil Kunnil, Vishal" <vishalo@qti.qualcomm.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
As reported by Vishal, the new backtrace output would be more useful if
it did not contain the full absolute path of each module in the list.
So strip off everything up to the last forward slash or backslash in the
string.
Example output:
IRQ Exception at 0x000000005EF110E0
DxeCore.dll loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EF121F0) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EF1289C) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEFB6B4) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEFAA44) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEFB450) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEF938C) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEF8D04) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEFA8E8) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEF3C14) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEF3E48) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EF0C838) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEEF70C) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEEE93C) loaded at 0x000000005EEED000
called from DxeCore.dll (0x000000005EEEE024) loaded at 0x000000005EEED000
Suggested-by: "Oliyil Kunnil, Vishal" <vishalo@qti.qualcomm.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
For historical reasons, the files under ArmLib are split up into 'common'
files under Common/, containing common C files as well as AArch64 and Arm
specific asm files, and ArmV7 and AArch64 files under ArmV7/ and AArch64/,
respectively. This presumably dates back to the time when ArmLib supported
different revisions of the 32-bit architecture (i.e., pre-V7)
Since the PI spec requires V7 or later, we can simplify this to Arm/ and
AArch64, which aligns ArmLib with the majority of other modules that carry
ARM or AArch64 specific code.
So move the files around so that shared files live at the same level as
ArmBaseLib.inf, and ARM/AArch64 specific files live in Arm/ or AArch64/,
respectively.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The ArmBaseLib timer code does not depend on MemoryAllocationLib at
all, so remove the #includes referring to it.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
This removes the following ArmLib implementation, which were, apart from
the fact that they targeted either ARM or AARCH64, fully identical:
ArmPkg/Library/ArmLib/AArch64/AArch64Lib.inf
ArmPkg/Library/ArmLib/AArch64/AArch64LibPei.inf
ArmPkg/Library/ArmLib/AArch64/AArch64LibPrePi.inf
ArmPkg/Library/ArmLib/AArch64/AArch64LibSec.inf
ArmPkg/Library/ArmLib/ArmV7/ArmV7Lib.inf
ArmPkg/Library/ArmLib/ArmV7/ArmV7LibPrePi.inf
ArmPkg/Library/ArmLib/ArmV7/ArmV7LibSec.inf
Only ArmBaseLib remains, which can fulfil the dependencies upon each of
the listed flavors.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Introduce a new ArmLib version ArmBaseLib, which encapsulates the ARM
version ArmV7Lib and the AArch64 version AArch64Lib.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Remove the NULL instance of ArmLib: it is not currently used, and its
usefulness its dubious.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
According to the ACPI 6.0/6.1 spec, the physical base address of GICC,
GICD, GICR and GIC ITS is 64-bit. So change the type of the various GIC
base address PCDs to 64-bit, and fix up all users.
Contributed-under: TianoCore Contribution Agreement 1.0
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Dennis Chen <dennis.chen@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
When dumping the CPU state after an unhandled fault, walk the stack
frames and decode the return addresses so we can show a minimal
backtrace. Unfortunately, we do not have sufficient information to
show the function names, but at least we can see the modules and the
return addresses inside the modules.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Clang does not like separate definitions for the __alias__ and the
__weak__ attributes, so merge the definitions into one.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
After the recent update of CompilerIntrinsicsLib, our memset() is no
longer emitted as a weak symbol. On ARM, this may cause problems when
combining this library with another library that supplies memset() [e.g.,
CryptoPkg/IntrinsicLib], due to the fact that the object also supplies
the __aeabi_memXXX entry points, which can only be satisfied by this
object. So make our memset() weak again, to let the other implementation
take precedence.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
BaseMemoryLib has recently been extended with an API function
IsZeroBuffer(), so copy the default implementation into BaseMemoryLibStm
as well.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
BaseMemoryLib has recently been extended with an API function
IsZeroGuid(), so copy the default implementation into BaseMemoryLibStm
as well.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
The BaseMemoryLibVstm implementation of BaseMemoryLib is ARM only, uses
the NEON register file despite the fact that the UEFI spec does not allow
it, and is currently not used anywhere. So remove it.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
This replaces the various implementations of memset and memcpy,
including the ARM RTABI ones (__aeabi_mem[set|clr]_[|4|8]) with
a single C implementation for each. The ones we have are either not
very sophisticated (ARM), or they are too sophisticated (memcpy() on
AARCH64, which may perform unaligned accesses) or already coded in C
(memset on AArch64).
The Tianocore codebase mandates the explicit use of its SetMem() and
CopyMem() equivalents, of which various implementations exist for use
in different contexts (PEI, DXE). Few compiler generated references to
these functions should remain, and so our implementations in this BASE
library should be small and usable with the MMU off.
So replace them with a simple C implementation that builds correctly
on GCC/AARCH64, CLANG/AARCH64, GCC/ARM, CLANG/ARM and RVCT/ARM.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections. Note that in some cases, various entry points
refer to different parts of the same routine, so in those cases,
the files have been left untouched.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Annotate functions with ASM_FUNC() so that they are emitted into
separate sections.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Ard Biesheuvel
Daniil Egranov
Laszlo Ersek
Gary Lin
Ruiyu Ni
Kurt Kennett
Dennis Chen