Re: spi-rspi I/O errors

[Simon Horman <horms@verge.net.au>]

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 -- geert@linux-m68k.org
> 
> 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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