Re: [PATCH v2 0/3] drm/prime: Only call dma_map_sgtable() for devices with DMA support

[Thomas Zimmermann <tzimmermann@suse.de>]

[-- Attachment #1.1: Type: text/plain, Size: 3373 bytes --]

Hi

Am 22.02.21 um 14:09 schrieb Christian König:
> 
> 
> Am 22.02.21 um 13:43 schrieb Thomas Zimmermann:
>> USB-based drivers cannot use DMA, so the importing of dma-buf attachments
>> currently fails for udl and gm12u320. This breaks joining/mirroring of
>> displays.
>>
>> The fix is now a little series. To solve the issue on the importer
>> side (i.e., the affected USB-based driver), patch 1 introduces a new
>> PRIME callback, struct drm_driver.gem_prime_create_object, which creates
>> an object and gives more control to the importing driver. Specifically,
>> udl and gm12u320 can now avoid the creation of a scatter/gather table
>> for the imported pages. Patch 1 is self-contained in the sense that it
>> can be backported into older kernels.
> 
> Mhm, that sounds like a little overkill to me.
> 
> Drivers can already import the DMA-bufs all by them selves without the 
> help of the DRM functions. See amdgpu for an example.
> 
> Daniel also already noted to me that he sees the DRM helper as a bit 
> questionable middle layer.

And this bug proves that it is. :)

> 
> Have you thought about doing that instead?

There appears to be some useful code in drm_gem_prime_import_dev(). But 
if the general sentiment goes towards removing 
gem_prime_import_sg_table, we can work towards that as well.

Best regards
Thomas

> 
> Christian.
> 
>>
>> Patches 2 and 3 update SHMEM and CMA helpers to use the new callback.
>> Effectively this moves the sg table setup from the PRIME helpers into
>> the memory managers. SHMEM now supports devices without DMA support,
>> so custom code can be removed from udl and g12u320.
>>
>> Tested by joining/mirroring displays of udl and radeon under Gnome/X11.
>>
>> v2:
>>     * move fix to importer side (Christian, Daniel)
>>     * update SHMEM and CMA helpers for new PRIME callbacks
>>
>> Thomas Zimmermann (3):
>>    drm: Support importing dmabufs into drivers without DMA
>>    drm/shmem-helper: Implement struct drm_driver.gem_prime_create_object
>>    drm/cma-helper: Implement struct drm_driver.gem_prime_create_object
>>
>>   drivers/gpu/drm/drm_gem_cma_helper.c    | 62 ++++++++++++++-----------
>>   drivers/gpu/drm/drm_gem_shmem_helper.c  | 38 ++++++++++-----
>>   drivers/gpu/drm/drm_prime.c             | 43 +++++++++++------
>>   drivers/gpu/drm/lima/lima_drv.c         |  2 +-
>>   drivers/gpu/drm/panfrost/panfrost_drv.c |  2 +-
>>   drivers/gpu/drm/panfrost/panfrost_gem.c |  6 +--
>>   drivers/gpu/drm/panfrost/panfrost_gem.h |  4 +-
>>   drivers/gpu/drm/pl111/pl111_drv.c       |  8 ++--
>>   drivers/gpu/drm/v3d/v3d_bo.c            |  6 +--
>>   drivers/gpu/drm/v3d/v3d_drv.c           |  2 +-
>>   drivers/gpu/drm/v3d/v3d_drv.h           |  5 +-
>>   include/drm/drm_drv.h                   | 12 +++++
>>   include/drm/drm_gem_cma_helper.h        | 12 ++---
>>   include/drm/drm_gem_shmem_helper.h      |  6 +--
>>   14 files changed, 120 insertions(+), 88 deletions(-)
>>
>> -- 
>> 2.30.1
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]