linux-kernel - Re: Are media drivers abusing of GFP_DMA? - was: Re: [LSF/MM TOPIC NOTES] x86 ZONE

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Date:   Mon, 14 May 2018 08:00:37 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Jean Christophe TROTIN <jean-christophe.trotin@...com>,
        Yasunari Takiguchi <Yasunari.Takiguchi@...y.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: Are media drivers abusing of GFP_DMA? - was: Re: [LSF/MM TOPIC
 NOTES] x86 ZONE_DMA love



On 07/05/18 17:19, Mauro Carvalho Chehab wrote:
> Em Mon, 07 May 2018 16:26:08 +0300
> Laurent Pinchart <laurent.pinchart@...asonboard.com> escreveu:
>
>> Hi Mauro,
>>
>> On Saturday, 5 May 2018 19:08:15 EEST Mauro Carvalho Chehab wrote:
>>> There was a recent discussion about the use/abuse of GFP_DMA flag when
>>> allocating memories at LSF/MM 2018 (see Luis notes enclosed).
>>>
>>> The idea seems to be to remove it, using CMA instead. Before doing that,
>>> better to check if what we have on media is are valid use cases for it, or
>>> if it is there just due to some misunderstanding (or because it was
>>> copied from some other code).
>>>
>>> Hans de Goede sent us today a patch stopping abuse at gspca, and I'm
>>> also posting today two other patches meant to stop abuse of it on USB
>>> drivers. Still, there are 4 platform drivers using it:
>>>
>>> 	$ git grep -l -E "GFP_DMA\\b" drivers/media/
>>> 	drivers/media/platform/omap3isp/ispstat.c
>>> 	drivers/media/platform/sti/bdisp/bdisp-hw.c
>>> 	drivers/media/platform/sti/hva/hva-mem.c

Hi Mauro,

The two STI drivers (bdisp-hw.c and hva-mem.c) are only expected to run 
on ARM platforms, not on x86.
Since this thread deals with x86 & DMA trouble, I am not sure that we 
actually have a problem for the sti drivers.

There are some other sti drivers that make use of this GFP_DMA flag 
(drivers/gpu/drm/sti/sti_*.c) and it does not seem to be a problem.

Nevertheless I can see that the media sti drivers depend on COMPILE_TEST 
(which is not the case for the DRM ones).
Would it be an acceptable solution to remove the COMPILE_TEST dependency?

BR

Fabien

>>> 	drivers/media/spi/cxd2880-spi.c
>>>
>>> Could you please check if GFP_DMA is really needed there, or if it is
>>> just because of some cut-and-paste from some other place?
>> I started looking at that for the omap3isp driver but Sakari beat me at
>> submitting a patch. GFP_DMA isn't needed for omap3isp.
>>
> Thank you both for looking into it.
>
> Regards,
> Mauro
>
>
>
> Thanks,
> Mauro