linux-kernel - [PATCH] atmel_spi: work-around required for new HW bug in AT91SAM9263 Rev.B SPI controller

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Message-Id: <1225711497-12913-1-git-send-email-haavard.skinnemoen@atmel.com>
Date:	Mon,  3 Nov 2008 12:24:57 +0100
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	David Brownell <david-b@...bell.net>
Cc:	spi-devel-general@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	Jean-Christophe Lallemand <jcl@...eltech.com>,
	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
Subject: [PATCH] atmel_spi: work-around required for new HW bug in AT91SAM9263 Rev.B SPI controller

From: Jean-Christophe Lallemand <jcl@...eltech.com>

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 <haavard.skinnemoen@...el.com>
---
 drivers/spi/atmel_spi.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/spi/atmel_spi.c b/drivers/spi/atmel_spi.c
index 02f9320..8abae4a 100644
--- a/drivers/spi/atmel_spi.c
+++ b/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);
 
-- 
1.5.6.5

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