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

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Message-ID: <3561479.qPIcrWnXEC@avalon>
Date:   Mon, 07 May 2018 16:26:08 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Cc:     Fabien Dessenne <fabien.dessenne@...com>,
        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-kernel@...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

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
> 	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.

-- 
Regards,

Laurent Pinchart