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SubjectRe: [PATCH] mtd: m25p80: make command buffer DMA-safe
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On Wed, 2009-10-28 at 14:21 +0100, Johannes Stezenbach wrote:
> spi_write() requires the buffer to be DMA-safe, kmalloc()
> it seperately to ensure this.
>
> Signed-off-by: Johannes Stezenbach <js@sig21.net>
>
>
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index 4c19269..21dd4d9 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -79,7 +79,7 @@ struct m25p {
> struct mtd_info mtd;
> unsigned partitioned:1;
> u8 erase_opcode;
> - u8 command[CMD_SIZE + FAST_READ_DUMMY_BYTE];
> + u8 *command;
> };
>
> static inline struct m25p *mtd_to_m25p(struct mtd_info *mtd)
> @@ -770,6 +770,11 @@ static int __devinit m25p_probe(struct spi_device *spi)
> flash = kzalloc(sizeof *flash, GFP_KERNEL);
> if (!flash)
> return -ENOMEM;
> + flash->command = kmalloc(CMD_SIZE + FAST_READ_DUMMY_BYTE, GFP_KERNEL);
> + if (!flash->command) {
> + kfree(flash);
> + return -ENOMEM;
> + }

Even though it is just 4 or 5 bytes it can do DMA? Does not sound too
sane to use DMA in that case. Does this patch fix a real error?

I do not know much about SPI, but for me it sounds like there should be
a method to ask SPI to avoid using DMA, and you should use that method.

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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