atmel_spi: work-around required for new HW bug in AT91SAM9263 Rev.B S…

…PI controller

We're working with an AT91SAM9263 Rev B in our design and I experienced
some inconsistency in spi-based touchscreen usage between our board and
the Atmel evaluation kit we have that runs on a Rev A chip.

The data was apparently delayed by 1 byte and got ridiculous data out of
the touchscreen driver, very strange.  As everything looked normal in
the spi, touchscreen and dma logs, I contacted the Atmel support and
they triggered me on a new HW bug that appeared in the Rev B SPI
controller.

The problem is that the SPI controller on the Rev B needs that the
software reset is performed two times so that it's performed correctly.

Applying the patch below solves the issue on my Rev B board.  I've tested
it as well on my Rev A evaluation kit and it has apparently no unwanted
side effect, things continue to work as expected.

Signed-off-by: Haavard Skinnemoen <[email protected]>
Cc: David Brownell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

drivers/spi/atmel_spi.c

@@ -766,6 +766,7 @@ static int __init atmel_spi_probe(struct platform_device *pdev)
 	/* Initialize the hardware */
 	clk_enable(clk);
 	spi_writel(as, CR, SPI_BIT(SWRST));
+	spi_writel(as, CR, SPI_BIT(SWRST)); /* AT91SAM9263 Rev B workaround */
 	spi_writel(as, MR, SPI_BIT(MSTR) | SPI_BIT(MODFDIS));
 	spi_writel(as, PTCR, SPI_BIT(RXTDIS) | SPI_BIT(TXTDIS));
 	spi_writel(as, CR, SPI_BIT(SPIEN));
@@ -782,6 +783,7 @@ static int __init atmel_spi_probe(struct platform_device *pdev)
 
 out_reset_hw:
 	spi_writel(as, CR, SPI_BIT(SWRST));
+	spi_writel(as, CR, SPI_BIT(SWRST)); /* AT91SAM9263 Rev B workaround */
 	clk_disable(clk);
 	free_irq(irq, master);
 out_unmap_regs:
@@ -805,6 +807,7 @@ static int __exit atmel_spi_remove(struct platform_device *pdev)
 	spin_lock_irq(&as->lock);
 	as->stopping = 1;
 	spi_writel(as, CR, SPI_BIT(SWRST));
+	spi_writel(as, CR, SPI_BIT(SWRST)); /* AT91SAM9263 Rev B workaround */
 	spi_readl(as, SR);
 	spin_unlock_irq(&as->lock);