2009-10-28 13:21:47

by Johannes Stezenbach

Subject: [PATCH] mtd: m25p80: make command buffer DMA-safe

spi_write() requires the buffer to be DMA-safe, kmalloc()
it seperately to ensure this.

Signed-off-by: Johannes Stezenbach <[email protected]>


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;
+ }

flash->spi = spi;
mutex_init(&flash->lock);
@@ -888,8 +893,10 @@ static int __devexit m25p_remove(struct spi_device *spi)
status = del_mtd_partitions(&flash->mtd);
else
status = del_mtd_device(&flash->mtd);
- if (status == 0)
+ if (status == 0) {
+ kfree(flash->command);
kfree(flash);
+ }
return 0;
}

2009-11-03 06:36:41

by Artem Bityutskiy

Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe

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 <[email protected]>
>
>
> 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)

2009-11-03 09:58:52

by Johannes Stezenbach

Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe

On Tue, Nov 03, 2009 at 08:36:05AM +0200, Artem Bityutskiy wrote:
> 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.
>
> 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.

It fixes a real error -- with an out-of-tree driver and ancient kernel.
For the flash read/write case it is used with list-DMA (e.g. write 4 bytes,
read 64KB). There are extensive comments in include/linux/spi/spi.h
which document the DMA-safe requirement of the buffers.

Thanks
Johannes

2009-11-10 14:54:54

by Artem Bityutskiy

Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe

On Tue, 2009-11-03 at 11:00 +0100, Johannes Stezenbach wrote:
> On Tue, Nov 03, 2009 at 08:36:05AM +0200, Artem Bityutskiy wrote:
> > 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.
> >
> > 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.
>
> It fixes a real error -- with an out-of-tree driver and ancient kernel.
> For the flash read/write case it is used with list-DMA (e.g. write 4 bytes,
> read 64KB). There are extensive comments in include/linux/spi/spi.h
> which document the DMA-safe requirement of the buffers.

Pushed to my l2-mtd-2.6 tree, thanks.

--
Best Regards,
Artem Bityutskiy (Артём Битюцкий)