RE: [BUG] spi/spi-atmel: DMA rx buffer corruption withSPI_IOC_MESSAGE

[Yang, Wenyou]

> -----Original Message-----
> From: Richard Genoud [mailto:richard.genoud@xxxxxxxxx]
> Sent: 2013å10æ21æ 16:26
> To: Yang, Wenyou
> Cc: linux-spi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Ferre, Nicolas;
> Mark Brown
> Subject: Re: [BUG] spi/spi-atmel: DMA rx buffer corruption with
> SPI_IOC_MESSAGE
> 
> 2013/10/21 Yang, Wenyou <Wenyou.Yang@xxxxxxxxx>:
> > Hi Richard,
> >
> >> -----Original Message-----
> >> From: Richard Genoud [mailto:richard.genoud@xxxxxxxxx]
> >> Sent: 2013å10æ17æ 19:01
> >> To: Yang, Wenyou
> >> Cc: linux-spi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Ferre,
> Nicolas;
> >> Mark Brown
> >> Subject: Re: [BUG] spi/spi-atmel: DMA rx buffer corruption with
> >> SPI_IOC_MESSAGE
> >>
> >> 2013/10/8 Richard Genoud <richard.genoud@xxxxxxxxx>:
> >> > Hi all,
> >> >
> >> > I finally found the bug I saw months ago, before "[PATCH v8 3/8]
> >> > spi/spi-atmel: add dmaengine support" was merged.
> >> >
> >> > Here it is:
> >> >
> >> > When the ioctl SPI_IOC_MESSAGE is used with small and big buffers,
> >> > the big RX buffer is corrupted with bytes from the big TX buffer.
> >> > (Small means size < DMA_MIN_BYTES, Big means size >
> >> DMA_MIN_BYTES)
> >> >
> >> > I'm attaching the test software that I used ( ./spi_test /dev/spidevx.x )
> >> >
> >> > It fills 3 TX buffers with 0xAA pattern: a small, a big and a small again.
> >> > It reads in return 3 RX buffers.
> >> > The MISO pin has to be on 3.3v.
> >> >
> >> > It checks if the received buffers are filled with 0xFF (they should
> >> > be, as MISO is high).
> >> > And I've got a lot of buffers filled partially with 0xAA bytes.
> >> >
> >> > BUT, if you apply this patch:
> >> > ---8<----
> >> > diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
> >> > index 83cf609..cde42a4 100644
> >> > --- a/drivers/spi/spi-atmel.c
> >> > +++ b/drivers/spi/spi-atmel.c
> >> > @@ -187,7 +187,7 @@
> >> >  /* use PIO for small transfers, avoiding DMA setup/teardown
> overhead
> >> and
> >> >   * cache operations; better heuristics consider wordsize and
> bitrate.
> >> >   */
> >> > -#define DMA_MIN_BYTES  16
> >> > +#define DMA_MIN_BYTES  0
> >> >
> >> >  struct atmel_spi_dma {
> >> >         struct dma_chan                 *chan_rx;
> >> > ---8<----
> >> > There's no error any more.
> >> > So there's something wrong happening when switching from/to pio
> >> > transfer to/from DMA.
> >> >
> >> > We didn't saw that at the time of the merge because we did the test
> >> > with a loop on MISO/MOSI,
> >> > so the RX buffer was corrupted with identical bytes.
> >> >
> >> > Best regards,
> >> > Richard.
> >>
> >> Hi Wenyou,
> >>
> >> Did you have the opportunity to give it a test ?
> >>
> >> Thread: https://lkml.org/lkml/2013/10/8/329
> > I tried to reproduce it with this thread, but I didn't
> > Which slave device did you use?
> 
> Hi Wenyou,
> 
> I'm not using any slave device, I'm just setting the MISO pin to 3.3V,
> then I execute the C code ( https://lkml.org/lkml/2013/10/8/329 )
> So, we should only receive 0xFF in the buffer.
> But i'm getting :
> aa aa aa aa aa aa aa aa aa aa aa aa aa aa ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff
> aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
> aa aa aa aa aa aa aa aa aa aa aa aa aa aa ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ff ff ff ff ff ff ff ff
> 
Hi, Richard,

The bug is reproduced.
Tested on at91sam9g25ek, Linux-3.6.9.

> Richard.

Best Regards,
Wenyou Yang
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