[PATCH xf86-video-amdgpu] Store FB for each CRTC in drmmode_flipdata_rec

[Michel Dänzer]

On 2018-07-30 08:12 PM, Alex Deucher wrote:
> On Fri, Jul 27, 2018 at 12:04 PM, Michel Dänzer <michel at daenzer.net> wrote:
>> From: Michel Dänzer <michel.daenzer at amd.com>
>>
>> We were only storing the FB provided by the client, but on CRTCs with
>> TearFree enabled, we use a separate FB. This could cause
>> drmmode_flip_handler to fail to clear drmmode_crtc->flip_pending, which
>> could result in a hang when waiting for the pending flip to complete. We
>> were trying to avoid that by always clearing drmmode_crtc->flip_pending
>> when TearFree is enabled, but that wasn't reliable, because
>> drmmode_crtc->tear_free can already be FALSE at this point when
>> disabling TearFree.
>>
>> Now that we're keeping track of each CRTC's flip FB separately,
>> drmmode_flip_handler can reliably clear flip_pending, and we no longer
>> need the TearFree hack.
>>
>> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
>>
>> [...]
>>
>> @@ -82,6 +81,7 @@ typedef struct {
>>         xf86CrtcPtr fe_crtc;
>>         amdgpu_drm_handler_proc handler;
>>         amdgpu_drm_abort_proc abort;
>> +       struct drmmode_fb *fb[0];
> 
> Don't some compilers have problems with zero sized arrays?

Are you thinking of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5b7d245009e734588e553092f5c0b0bd788b3a55
? Per https://bugs.freedesktop.org/show_bug.cgi?id=66932#c24 , the
problem there was variable sized arrays being declared as [1], which
obviously can't work.

Declaring a [0] array at the end of a struct is a GCC extension, see
https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero-Length . clang
seems to handle this fine as well.

An alternative would be using the C99 syntax "[];" instead, but I think
the above is fine in this case.


> Other than that looks good to me:
> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>

Thanks!


-- 
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