Re: [PATCH] mtd: devices: m25p80: Make the buffer passed in op is DMA-able

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Mon, 17 Sep 2018 17:13:32 +0300
Jarkko Nikula <jarkko.nikula@linux.intel.com> wrote:

> On 09/17/2018 04:36 PM, Boris Brezillon wrote:
> > As documented in spi-mem.h, spi_mem_op->data.buf.{in,out} must be
> > DMA-able, and commit 4120f8d158ef ("mtd: spi-nor: Use the spi_mem_xx()
> > API") failed to follow this rule as buffers passed to  
> > ->{read,write}_reg() are usually placed on the stack.  
> > 
> > Fix that by allocating a scratch buffer and copying the data in there
> > before passing it to the spi-mem layer.
> > 
> > Fixes: 4120f8d158ef ("mtd: spi-nor: Use the spi_mem_xx() API")
> > Reported-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > ---
> > Note that the ->{read,write}() path is still buggy since nothing
> > guarantees that buffers passed by the MTD layer to the SPI NOR layer
> > are DMA-able, but this is a long-standing issue which we'll have to
> > address at the spi-nor level (this layer can choose the bounce buffer
> > size based on nor->page_size).
> > ---
> >   drivers/mtd/devices/m25p80.c | 24 +++++++++++++++++++++---
> >   1 file changed, 21 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> > index cbfafc453274..3b7fafa4bbd6 100644
> > --- a/drivers/mtd/devices/m25p80.c
> > +++ b/drivers/mtd/devices/m25p80.c
> > @@ -39,14 +39,22 @@ static int m25p80_read_reg(struct spi_nor *nor, u8 code, u8 *val, int len)
> >   	struct spi_mem_op op = SPI_MEM_OP(SPI_MEM_OP_CMD(code, 1),
> >   					  SPI_MEM_OP_NO_ADDR,
> >   					  SPI_MEM_OP_NO_DUMMY,
> > -					  SPI_MEM_OP_DATA_IN(len, val, 1));
> > +					  SPI_MEM_OP_DATA_IN(len, NULL, 1));
> > +	void *scratchbuf;
> >   	int ret;
> >   
> > +	scratchbuf = kmemdup(val, len, GFP_KERNEL);
> > +	if (!scratchbuf)
> > +		return -ENOMEM;
> > +
> > +	op.data.buf.in = scratchbuf;
> >   	ret = spi_mem_exec_op(flash->spimem, &op);
> >   	if (ret < 0)
> >   		dev_err(&flash->spimem->spi->dev, "error %d reading %x\n", ret,
> >   			code);
> >   
> > +	kfree(scratchbuf);
> > +  
> 
> Actually this makes things even worse: "unrecognized JEDEC id bytes: b1, 
> 74, 01" since we don't copy scratchbuf to original buffer and kmemdup 
> before bus read is needless :-)

True :-).

I'll fix that and send a v2.