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

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Date:   Tue, 26 Dec 2017 19:12:09 +0530
From:   Vignesh R <vigneshr@...com>
To:     Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        <computersforpeace@...il.com>, <dwmw2@...radead.org>,
        <richard@....at>, <boris.brezillon@...e-electrons.com>,
        <marek.vasut@...il.com>, <linux-mtd@...ts.infradead.org>,
        <broonie@...nel.org>, <linux@...linux.org.uk>
CC:     <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

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