linux-kernel - Re: DMA-buf and uncached system memory

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Message-ID: <4988ab02-dbdb-e452-7106-771c2a1ebbca@suse.de>
Date:   Thu, 23 Jun 2022 10:42:49 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Christian König <christian.koenig@....com>,
        linux-media <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linaro-mm-sig@...ts.linaro.org, lkml <linux-kernel@...r.kernel.org>
Cc:     "Sharma, Shashank" <Shashank.Sharma@....com>
Subject: Re: DMA-buf and uncached system memory

Hi

Am 23.06.22 um 10:26 schrieb Christian König:
> Am 23.06.22 um 10:13 schrieb Thomas Zimmermann:
>> Hi Christian
>>
>> Am 15.02.21 um 09:58 schrieb Christian König:
>>> Hi guys,
>>>
>>> we are currently working an Freesync and direct scan out from system 
>>> memory on AMD APUs in A+A laptops.
>>>
>>> On problem we stumbled over is that our display hardware needs to 
>>> scan out from uncached system memory and we currently don't have a 
>>> way to communicate that through DMA-buf.
>>>
>>> For our specific use case at hand we are going to implement something 
>>> driver specific, but the question is should we have something more 
>>> generic for this?
>>
>> I had a patchset here that extends iosys-map (former dma-buf-map) with 
>> caching information. I'll post a copy.
> 
> Oh, nice. But why on iosys-map? We need that per DMA-buf.

It's returned via the dma-buf's vmap call within the iosys-map 
structure. If the dma-buf moves, the following vmap calls always return 
updated caching information. Maybe it's not quite what you need for 
Freesync?

I'll use this for format-conversion helpers, which do some optimizations 
for uncached memory.

Anyway, I have to look for that patch...

Best regards
Thomas

> 
> Thanks,
> Christian.
> 
>>
>> Sorry for being late to reply.
>>
>> Best regards
>> Thomas
>>
>>>
>>> After all the system memory access pattern is a PCIe extension and as 
>>> such something generic.
>>>
>>> Regards,
>>> Christian.
>>> _______________________________________________
>>> dri-devel mailing list
>>> dri-devel@...ts.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>>
> 

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

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