Re: [PATCH v2 0/5] Add option to mmap GEM buffers cached

Paul Cercueil
2021-03-10T19:03:13Z

Hi Thomas,

Le lun. 8 mars 2021 à 9:41, Thomas Zimmermann <tzimmermann@suse.de> a
écrit :
> Hi Paul,
>
> having individual functions for each mode only makes sense if the
> decision is at compile time. But in patch 5, you're working around
> your earlier design by introducing in-driver helpers that select the
> correct CMA function.
>
> In SHMEM helpers we have the flag map_wc in the GEM structure that
> selects the pages caching mode (wc vs uncached). I think CMA should
> use this design as well. Have a map_noncoherent flag in the CMA GEM
> object and set it from the driver's implementation of
> gem_create_object.

Is that a new addition? That severely reduces the patchset size, which
is perfect.

I'll send a V3 then.

Cheers,
-Paul

> And in the long run, we could try to consolidate all drivers/helpers
> mapping flags in struct drm_gem_object.
>
> Best regards
> Thomas
>
> Am 07.03.21 um 21:28 schrieb Paul Cercueil:
>> Rework of my previous patchset which added support for GEM buffers
>> backed by non-coherent memory to the ingenic-drm driver.
>>
>> Having GEM buffers backed by non-coherent memory is interesting in
>> the particular case where it is faster to render to a non-coherent
>> buffer then sync the data cache, than to render to a write-combine
>> buffer, and (by extension) much faster than using a shadow buffer.
>> This is true for instance on some Ingenic SoCs, where even simple
>> blits (e.g. memcpy) are about three times faster using this method.
>>
>> For the record, the previous patchset was accepted for 5.10 then had
>> to be reverted, as it conflicted with some changes made to the DMA
>> API.
>>
>> This new patchset is pretty different as it adds the functionality to
>> the DRM core. The first three patches add variants to existing
>> functions
>> but with the "non-coherent memory" twist, exported as GPL symbols.
>> The
>> fourth patch adds a function to be used with the damage helpers.
>> Finally, the last patch adds support for non-coherent GEM buffers to
>> the
>> ingenic-drm driver. The functionality is enabled through a module
>> parameter, and is disabled by default.
>>
>> Cheers,
>> -Paul
>>
>> Paul Cercueil (5):
>> drm: Add and export function drm_gem_cma_create_noncoherent
>> drm: Add and export function drm_gem_cma_dumb_create_noncoherent
>> drm: Add and export function drm_gem_cma_mmap_noncoherent
>> drm: Add and export function drm_gem_cma_sync_data
>> drm/ingenic: Add option to alloc cached GEM buffers
>>
>> drivers/gpu/drm/drm_gem_cma_helper.c | 223
>> +++++++++++++++++++---
>> drivers/gpu/drm/ingenic/ingenic-drm-drv.c | 49 ++++-
>> drivers/gpu/drm/ingenic/ingenic-drm.h | 4 +
>> drivers/gpu/drm/ingenic/ingenic-ipu.c | 14 +-
>> include/drm/drm_gem_cma_helper.h | 13 ++
>> 5 files changed, 273 insertions(+), 30 deletions(-)
>>
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
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>