[Openpvrsgx-devgroup] Reverse engineering SGX 540 userspace driver
lucas.fryzek at hazeco.xyz
Fri Nov 12 05:18:57 CET 2021
> Hello Nikolaus,
>> It *could* work but was never tested. We have the matching DDK
>> release version in the tree. Just choose
>> It may be that the branch is missing some fixes that have been
>> applied to the versions CONFIG_PVRSGX_1_14_3699939 and
>> CONFIG_PVRSGX_1_17_4948957 which are more or less well running on
>> Do you have the user space for 1.14.3759903? I am not sure but it
>> may be stored in the factory flash image.
>>> I'm trying to get a setup right now where I can compile a kernel
>>> mode driver and make modifications to get a better idea on how
>>> the GPU is being controlled. If I can use a more modern kernel
>>> and linux userland that would be very nice.
>> Just get the letux tree:
>> It includes everything incl. HDMI driver for the CI20 (use
>> letux_defconfig) and compiles the SGX driver that is configured.
>> But the default is CONFIG_PVRSGX_1_17_4948957=y so there may be
>> surprises when switching to CONFIG_PVRSGX_1_14_3759903 we can
>> discuss how to fix.
> I believe my board is currently flashed with the `Debian 8
> 2015-09-09` image from this webpage https://elinux.org/CI20_Distros.
> I took a look through the filesystem and I cannot find the DDK as a
> zip package, but all of the PVR libraries seem to be versioned as
> `1.14.544606452`. The reason I referred to `1.14.3759903` before was
> this is the version listed on this web page
> I'm not sure what the latest available kernel module + userland is
> for the CI20. I did find this git repo
> https://github.com/MIPS/CI20_PVR-prebuilts, that seems to have
> userland libraries for version `1.15.4568187`. But I'm not if there
> is a matching open source kernel driver for this repo.
> I am currently trying to get a setup where I can build the open PVR
> kernel module and have it work with the userspace. I've been working.
> Building my own kernel with the old debian images seems to break DRM,
> so I suspect there is so version mismatching going on. I'll take a
> look at the kernel in the letux project instead as this looks like a
> more productive use of my time. I'll also take a look at some of the
> older debian images for the CI20 to see if the `1.14.3759903` to
> attempt to use with the letux kernel.
So I managed to get the letux kernel building and running on my CI20.
Had a bit of trouble there where the prebuilt kernels don't see to run
properly on the CI20, but once I grabbed the latest kernel from github
and built that everything seemed to work fine. I managed to find the
`1.14.3759903` userland at this link
I changed the kernel config to build the kernel module version
`1.14.3759903`, there were several errors but I just looked at the
`1.17` version and copied the fixed from there. Unfortunately the
userland does not seem to be happy, I tried testing a few of the
applications and none of them seem to work. I ran `strace` on the
binaries and it looks like they call `DRM_IOCTL_VERSION`, are unhappy
with results and then error out saying they can't find a PVR GPU.
I think to do any effective reverse engineering of the GPU I'll need a
working userland, so it looks like I have a bit of work there :P The
DRM version error gives a path to start looking, so I'll try messing
with that and see where I can go from there.
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