On 3/13/19 11:54 AM, Christian König wrote:
> Am 13.03.19 um 16:38 schrieb Michel Dänzer:
>> On 2019-03-13 2:37 p.m., Christian König wrote:
>>> Am 13.03.19 um 14:31 schrieb Ville Syrjälä:
>>>> On Wed, Mar 13, 2019 at 10:35:08AM +0100, Michel Dänzer wrote:
>>>>> On 2019-03-12 6:15 p.m., Noralf Trønnes wrote:
>>>>>> Den 12.03.2019 17.17, skrev Ville Syrjälä:
>>>>>>> On Tue, Mar 12, 2019 at 11:47:04AM +0100, Michel Dänzer wrote:
>>>>>>>> On 2019-03-11 6:42 p.m., Noralf Trønnes wrote:
>>>>>>>>> This adds support for outputting kernel messages on panic().
>>>>>>>>> A kernel message dumper is used to dump the log. The dumper
>>>>>>>>> iterates
>>>>>>>>> over each DRM device and it's crtc's to find suitable
>>>>>>>>> framebuffers.
>>>>>>>>>
>>>>>>>>> All the other dumpers are run before this one except mtdoops.
>>>>>>>>> Only atomic drivers are supported.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
>>>>>>>>> ---
>>>>>>>>> [...]
>>>>>>>>>
>>>>>>>>> diff --git a/include/drm/drm_framebuffer.h
>>>>>>>>> b/include/drm/drm_framebuffer.h
>>>>>>>>> index f0b34c977ec5..f3274798ecfe 100644
>>>>>>>>> --- a/include/drm/drm_framebuffer.h
>>>>>>>>> +++ b/include/drm/drm_framebuffer.h
>>>>>>>>> @@ -94,6 +94,44 @@ struct drm_framebuffer_funcs {
>>>>>>>>> struct drm_file *file_priv, unsigned flags,
>>>>>>>>> unsigned color, struct drm_clip_rect *clips,
>>>>>>>>> unsigned num_clips);
>>>>>>>>> +
>>>>>>>>> + /**
>>>>>>>>> + * @panic_vmap:
>>>>>>>>> + *
>>>>>>>>> + * Optional callback for panic handling.
>>>>>>>>> + *
>>>>>>>>> + * For vmapping the selected framebuffer in a panic context.
>>>>>>>>> Must
>>>>>>>>> + * be super careful about locking (only trylocking allowed).
>>>>>>>>> + *
>>>>>>>>> + * RETURNS:
>>>>>>>>> + *
>>>>>>>>> + * NULL if it didn't work out, otherwise an opaque cookie
>>>>>>>>> which is
>>>>>>>>> + * passed to @panic_draw_xy. It can be anything: vmap area,
>>>>>>>>> structure
>>>>>>>>> + * with more details, just a few flags, ...
>>>>>>>>> + */
>>>>>>>>> + void *(*panic_vmap)(struct drm_framebuffer *fb);
>>>>>>>> FWIW, the panic_vmap hook cannot work in general with the
>>>>>>>> amdgpu/radeon
>>>>>>>> drivers:
>>>>>>>>
>>>>>>>> Framebuffers are normally tiled, writing to them with the CPU
>>>>>>>> results in
>>>>>>>> garbled output.
>>>>>>>>
>>>>>> In which case the driver needs to support the ->panic_draw_xy
>>>>>> callback,
>>>>>> or maybe it's possible to make a generic helper for tiled buffers.
>>>>> I'm afraid that won't help, at least not without porting big chunks of
>>>>> https://gitlab.freedesktop.org/mesa/mesa/tree/master/src/amd/addrlib
>>>>> into the kernel, none of which will be used for anything else.
>>>>>
>>>>>
>>>>>>>> There would need to be a mechanism for switching scanout to a
>>>>>>>> linear,
>>>>>>>> CPU accessible framebuffer.
>>>>>>> I suppose panic_vmap() could just provide a linear temp buffer
>>>>>>> to the panic handler, and panic_unmap() could copy the contents
>>>>>>> over to the real fb.
>>>>> Copy how? Using a GPU engine?
>>>> CPU maybe? Though I suppose that won't work if the buffer isn't CPU
>>>> accesible :/
>>> Well we do have a debug path for accessing invisible memory with the
>>> CPU.
>>>
>>> E.g. three registers: DATA and auto increment OFFSET_LO/HI. So you can
>>> just read/write DATA over and over again if you want to access some
>>> memory.
>> Right. I assume that'll be very slow, but I guess it could do when the
>> memory isn't directly CPU accessible.
>
> Just made a quick test and reading 33423360 bytes (4096x2040x4) using
> that interfaces takes about 13 seconds.
>
> IIRC we don't use the auto increment optimization yet, so that can
> probably be improved by a factor of 3 or more.
>
>>> But turning of tilling etc is still extremely tricky when the system is
>>> already unstable.
>> Maybe we could add a little hook to the display code, which just
>> disables tiling for scanout and maybe disables non-primary planes, but
>> doesn't touch anything else. Harry / Nicholas, does that seem feasible?
>>
>>
>> I'm coming around from "this is never going to work" to "it might
>> actually work" with our hardware...
>
> Yeah, agree. It's a bit tricky, but doable.
A "disable_tiling" hook or something along those lines could work for
display. It's a little bit non trivial when you want to start dealing
with locking and any active DRM commits, but we have a global lock
around all our hardware programming anyway that makes that easier to
deal with.
I think we can just re-commit and update the existing hardware state
with only the tiling info for every plane reset to off. For most buffers
I don't think we'd have to really consider changing anything else here
as long as you respect the current FB size and pitch.
Nicholas Kazlauskas
>
> Takeaway for Noralf is that this whole vmap on panic won't even remotely
> work. We need to get the data byte by byte without a page mapping if
> that is ever going to fly.
>
> Christian.
>
>>
>>
>
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