On Tue, Jan 07, 2014 at 09:27:18PM +0100, Geert Uytterhoeven wrote:
> I was regularly getting I/O errors when using the Renesas RSPI/QSPI
> driver on r8a7791:
>
> m25p80 spi0.0: error -110 reading SR
>
> Until I applied the following patch, which re-reads RSPI_SPSR on a time-out,
> and continues if the condition has become true:
>
> diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
> index 4b31d89e8568..e63e30c500da 100644
> --- a/drivers/spi/spi-rspi.c
> +++ b/drivers/spi/spi-rspi.c
> @@ -442,8 +442,13 @@ static int rspi_wait_for_interrupt(struct rspi_data
> *rspi, u8 wait_mask,
> rspi->spsr = rspi_read8(rspi, RSPI_SPSR);
> rspi_enable_irq(rspi, enable_bit);
> ret = wait_event_timeout(rspi->wait, rspi->spsr & wait_mask, HZ);
> - if (ret == 0 && !(rspi->spsr & wait_mask))
> - return -ETIMEDOUT;
> + if (ret == 0 && !(rspi->spsr & wait_mask)) {
> + u8 spsr = rspi_read8(rspi, RSPI_SPSR);
> + printk("*** rspi->spsr = 0x%02x, real spsr = 0x%02x, wait_mask
> = 0x%02x ***\n",
> + rspi->spsr, spsr, wait_mask);
> + if (!(spsr & wait_mask))
> + return -ETIMEDOUT;
I'm entirely unsure if this is the right approach,
but if it is should rspi->spsr = spsr go somewhere around here?
> + }
>
> return 0;
> }
>
> Now it prints from time to time:
>
> *** rspi->spsr = 0x20, real spsr = 0xa0, wait_mask = 0x80 ***
>
> which shows that rspi->spsr (as set from the interrupt handler) didn't
> have bit 7 set, while RSPI_SPSR does have bit 7 set.
>
> So this looks like a race condition in the interrupt handling.
>
> I didn't notice any data corruption after the patch.
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> [email protected]
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like
> that.
> -- Linus Torvalds
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