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

[Paul Cercueil]

Hi Thomas,

Le lun. 8 mars 2021 à 9:41, Thomas Zimmermann <tzimmermann@xxxxxxx> 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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