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

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Message-ID: <02699364973B424C83A42A84B04FDA854A3893@JPYOKXMS113.jp.sony.com>
Date:   Thu, 10 May 2018 04:39:58 +0000
From:   <Yasunari.Takiguchi@...y.com>
To:     <mchehab+samsung@...nel.org>, <laurent.pinchart@...asonboard.com>,
        <fabien.dessenne@...com>, <jean-christophe.trotin@...com>,
        <sakari.ailus@...ux.intel.com>
CC:     <mcgrof@...nel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <Yasunari.Takiguchi@...y.com>
Subject: RE: Are media drivers abusing of GFP_DMA? - was: Re: [LSF/MM TOPIC
 NOTES] x86 ZONE_DMA love

Dear Mauro

> -----Original Message-----
> 
> 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?
About drivers/media/spi/cxd2880-spi.c,
we referred to kmalloc of driver/spi/spi.c spi_write_then_read() function and made this code. 

Regards,
Takiguchi