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 14:59:00 +0100
From:   Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>
To:     Vignesh R <vigneshr@...com>, 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 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 ?

Best regards,

Cyrille