Fix Oops with Atmel SPI

On 2010-04-22 00:24:10, Andrew Morton wrote:
> Finally..  Wouldn't it be better to just fix the atmel SPI driver so
> that it doesn't barf when handed vmalloc'ed memory?  Who do we ridicule
> about that?  <checks, adds cc>

You mean something like this instead?

On Wed, 19 May 2010 13:05:00 +0200
Anders Larsen <al@alarsen.net> wrote:

> On 2010-04-22 00:24:10, Andrew Morton wrote:
> > Finally..  Wouldn't it be better to just fix the atmel SPI driver so
> > that it doesn't barf when handed vmalloc'ed memory?  Who do we ridicule
> > about that?  <checks, adds cc>
> 
> You mean something like this instead?

That looks simple enough.  How do we get it tested, changelogged and
merged up?  Haavard, can you please take a look?


> diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
> index c4e0442..a9ad5e8 100644
> --- a/drivers/spi/atmel_spi.c
> +++ b/drivers/spi/atmel_spi.c
> @@ -352,16 +352,30 @@ atmel_spi_dma_map_xfer(struct atmel_spi *as, struct spi_transfer *xfer)
>  
>  	xfer->tx_dma = xfer->rx_dma = INVALID_DMA_ADDRESS;
>  	if (xfer->tx_buf) {
> -		xfer->tx_dma = dma_map_single(dev,
> -				(void *) xfer->tx_buf, xfer->len,
> -				DMA_TO_DEVICE);
> +		if (is_vmalloc_addr(xfer->tx_buf))
> +			xfer->tx_dma = dma_map_page(dev,
> +					vmalloc_to_page(xfer->tx_buf),
> +					(unsigned long)xfer->tx_buf & (PAGE_SIZE-1),
> +					xfer->len,
> +					DMA_TO_DEVICE);
> +		else
> +			xfer->tx_dma = dma_map_single(dev,
> +					(void *) xfer->tx_buf, xfer->len,
> +					DMA_TO_DEVICE);
>  		if (dma_mapping_error(dev, xfer->tx_dma))
>  			return -ENOMEM;
>  	}
>  	if (xfer->rx_buf) {
> -		xfer->rx_dma = dma_map_single(dev,
> -				xfer->rx_buf, xfer->len,
> -				DMA_FROM_DEVICE);
> +		if (is_vmalloc_addr(xfer->rx_buf))
> +			xfer->rx_dma = dma_map_page(dev,
> +					vmalloc_to_page(xfer->rx_buf),
> +					(unsigned long)xfer->rx_buf & (PAGE_SIZE-1),
> +					xfer->len,
> +					DMA_FROM_DEVICE);
> +		else
> +			xfer->rx_dma = dma_map_single(dev,
> +					xfer->rx_buf, xfer->len,
> +					DMA_FROM_DEVICE);
>  		if (dma_mapping_error(dev, xfer->rx_dma)) {
>  			if (xfer->tx_buf)
>  				dma_unmap_single(dev,
>

Anders,

I just tested one path, the "if (xfer->rx_buf)...", on
2.6.33 plus the at91 patch
http://maxim.org.za/AT91RM9200/2.6/2.6.33-at91.patch.gz
running on AT91SAM9260.

The test case involved doing i/o via the /dev/mtdblock
interface -- but this only exercises the rx_buf/vmalloc path --
MTD reads a block into the cache-buf to merge the write data. Not 
sure that we have any use cases for the tx_buf path using MTD.

-Ian

On Friday 21 May 2010, Andrew Morton wrote:
> On Wed, 19 May 2010 13:05:00 +0200
>
> Anders Larsen <al@alarsen.net> wrote:
> > On 2010-04-22 00:24:10, Andrew Morton wrote:
> > > Finally..  Wouldn't it be better to just fix the atmel SPI
> > > driver so that it doesn't barf when handed vmalloc'ed
> > > memory?  Who do we ridicule about that?  <checks, adds cc>
> >
> > You mean something like this instead?
>
> That looks simple enough.  How do we get it tested,
> changelogged and merged up?  Haavard, can you please take a
> look?
>
> > diff --git a/drivers/spi/atmel_spi.c
> > b/drivers/spi/atmel_spi.c index c4e0442..a9ad5e8 100644
> > --- a/drivers/spi/atmel_spi.c
> > +++ b/drivers/spi/atmel_spi.c
> > @@ -352,16 +352,30 @@ atmel_spi_dma_map_xfer(struct
> > atmel_spi *as, struct spi_transfer *xfer)
> >
> >  	xfer->tx_dma = xfer->rx_dma = INVALID_DMA_ADDRESS;
> >  	if (xfer->tx_buf) {
> > -		xfer->tx_dma = dma_map_single(dev,
> > -				(void *) xfer->tx_buf, xfer->len,
> > -				DMA_TO_DEVICE);
> > +		if (is_vmalloc_addr(xfer->tx_buf))
> > +			xfer->tx_dma = dma_map_page(dev,
> > +					vmalloc_to_page(xfer->tx_buf),
> > +					(unsigned long)xfer->tx_buf & (PAGE_SIZE-1),
> > +					xfer->len,
> > +					DMA_TO_DEVICE);
> > +		else
> > +			xfer->tx_dma = dma_map_single(dev,
> > +					(void *) xfer->tx_buf, xfer->len,
> > +					DMA_TO_DEVICE);
> >  		if (dma_mapping_error(dev, xfer->tx_dma))
> >  			return -ENOMEM;
> >  	}
> >  	if (xfer->rx_buf) {
> > -		xfer->rx_dma = dma_map_single(dev,
> > -				xfer->rx_buf, xfer->len,
> > -				DMA_FROM_DEVICE);
> > +		if (is_vmalloc_addr(xfer->rx_buf))
> > +			xfer->rx_dma = dma_map_page(dev,
> > +					vmalloc_to_page(xfer->rx_buf),
> > +					(unsigned long)xfer->rx_buf & (PAGE_SIZE-1),
> > +					xfer->len,
> > +					DMA_FROM_DEVICE);
> > +		else
> > +			xfer->rx_dma = dma_map_single(dev,
> > +					xfer->rx_buf, xfer->len,
> > +					DMA_FROM_DEVICE);
> >  		if (dma_mapping_error(dev, xfer->rx_dma)) {
> >  			if (xfer->tx_buf)
> >  				dma_unmap_single(dev,

Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 19 May 2010 13:05:00 +0200
> Anders Larsen <al@alarsen.net> wrote:
> 
> > On 2010-04-22 00:24:10, Andrew Morton wrote:
> > > Finally..  Wouldn't it be better to just fix the atmel SPI driver so
> > > that it doesn't barf when handed vmalloc'ed memory?  Who do we ridicule
> > > about that?  <checks, adds cc>
> > 
> > You mean something like this instead?
> 
> That looks simple enough.  How do we get it tested, changelogged and
> merged up?  Haavard, can you please take a look?

Sure. Sorry for the late response; I've been traveling for the last two
weeks.

Did anyone check what other drivers do to handle this case? Surely this
isn't the only driver which supports DMA?

> > diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
> > index c4e0442..a9ad5e8 100644
> > --- a/drivers/spi/atmel_spi.c
> > +++ b/drivers/spi/atmel_spi.c
> > @@ -352,16 +352,30 @@ atmel_spi_dma_map_xfer(struct atmel_spi *as, struct spi_transfer *xfer)
> >  
> >  	xfer->tx_dma = xfer->rx_dma = INVALID_DMA_ADDRESS;
> >  	if (xfer->tx_buf) {
> > -		xfer->tx_dma = dma_map_single(dev,
> > -				(void *) xfer->tx_buf, xfer->len,
> > -				DMA_TO_DEVICE);
> > +		if (is_vmalloc_addr(xfer->tx_buf))
> > +			xfer->tx_dma = dma_map_page(dev,
> > +					vmalloc_to_page(xfer->tx_buf),
> > +					(unsigned long)xfer->tx_buf & (PAGE_SIZE-1),
> > +					xfer->len,
> > +					DMA_TO_DEVICE);

Ok, this should be fine for small transfers, but what happens if the
transfer crosses a page boundary? Are there any guarantees that this
will never happen? What callers are passing vmalloc'ed memory in the
first place?

Ditto for the rx path.

Haavard