linux-kernel - Re: [PATCH 1/3] mtd: spi-nor: add optional DMA-safe bounce buffer for data transfer

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Date:   Sun, 7 Jan 2018 21:07:03 +0100
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
Cc:     Vignesh R <vigneshr@...com>, computersforpeace@...il.com,
        dwmw2@...radead.org, richard@....at, marek.vasut@...il.com,
        linux-mtd@...ts.infradead.org, broonie@...nel.org,
        linux@...linux.org.uk, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, robh@...nel.org,
        devicetree@...r.kernel.org, nicolas.ferre@...rochip.com,
        radu.pirea@...rochip.com
Subject: Re: [PATCH 1/3] mtd: spi-nor: add optional DMA-safe bounce buffer
 for data transfer

On Tue, 26 Dec 2017 14:59:00 +0100
Cyrille Pitchen <cyrille.pitchen@...ev4u.fr> wrote:

> Hi Vignesh
> 
> Le 26/12/2017 à 14:42, Vignesh R a écrit :
> > Hi Cyrille,
> > 
> > Thanks for doing this series! One comment below.
> > 
> > On 24-Dec-17 10:06 AM, Cyrille Pitchen wrote:
> > [...]  
> >> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> >> index 8bafd462f0ae..59f9fbd45234 100644
> >> --- a/drivers/mtd/spi-nor/spi-nor.c
> >> +++ b/drivers/mtd/spi-nor/spi-nor.c
> >> @@ -14,8 +14,10 @@
> >>  #include <linux/errno.h>
> >>  #include <linux/module.h>
> >>  #include <linux/device.h>
> >> +#include <linux/highmem.h>
> >>  #include <linux/mutex.h>
> >>  #include <linux/math64.h>
> >> +#include <linux/mm.h>
> >>  #include <linux/sizes.h>
> >>  #include <linux/slab.h>
> >>  
> >> @@ -1232,6 +1234,56 @@ static const struct flash_info spi_nor_ids[] = {
> >>  	{ },
> >>  };
> >>  
> >> +static bool spi_nor_is_dma_safe(const void *buf)
> >> +{
> >> +	if (is_vmalloc_addr(buf))
> >> +		return false;
> >> +
> >> +#ifdef CONFIG_HIGHMEM
> >> +	if ((unsigned long)buf >= PKMAP_BASE &&
> >> +	    (unsigned long)buf < (PKMAP_BASE + (LAST_PKMAP * PAGE_SIZE)))
> >> +		return false;
> >> +#endif
> >> +
> >> +	return true;
> >> +}
> >> +  
> > 
> > Better way would be to use virt_addr_valid():
> > static bool spi_nor_is_dma_safe(const void *buf)
> > {
> > 	return virt_addr_valid(buf);
> > }
> > 
> > Regards
> > Vignesh
> >   
> 
> Thanks for the advice :)
> 
> https://patchwork.kernel.org/patch/9768341/
> Maybe I could check both virt_addr_valid() and object_is_on_stack() too ?

Yep, see the explanation given here [1].

[1]http://elixir.free-electrons.com/linux/v4.15-rc6/source/Documentation/DMA-API-HOWTO.txt#L132