Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754804Ab2K2Ooe (ORCPT ); Thu, 29 Nov 2012 09:44:34 -0500 Received: from mail-vb0-f46.google.com ([209.85.212.46]:56064 "EHLO mail-vb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750931Ab2K2Ood (ORCPT ); Thu, 29 Nov 2012 09:44:33 -0500 MIME-Version: 1.0 In-Reply-To: <1354165536-18529-2-git-send-email-ch.naveen@samsung.com> References: <1354165536-18529-1-git-send-email-ch.naveen@samsung.com> <1354165536-18529-2-git-send-email-ch.naveen@samsung.com> Date: Thu, 29 Nov 2012 23:44:32 +0900 X-Google-Sender-Auth: M-GB4sUAhj_1NvXAvwBaRyTN_jU Message-ID: Subject: Re: [PATCH 1/2] i2c-s3c2410: Leave the bus disabled unless it is in use From: Kyungmin Park To: Naveen Krishna Chatradhi Cc: linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-i2c@vger.kernel.org, grundler@chromium.org, sjg@chromium.org, naveen@chromium.org, w.sang@pengutronix.de, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5049 Lines: 132 Acked-by: Kyungmin Park On Thu, Nov 29, 2012 at 2:05 PM, Naveen Krishna Chatradhi wrote: > From: Simon Glass > > There is a rather odd feature of the exynos i2c controller that if it > is left enabled, it can lock itself up with the clk line held low. > This makes the bus unusable. > > Unfortunately, the s3c24xx_i2c_set_master() function does not notice > this, and reports a timeout. From then on the bus cannot be used until > the AP is rebooted. > > The problem happens when any sort of interrupt occurs (e.g. due to a > bus transition) when we are not in the middle of a transaction. We > have seen many instances of this when U-Boot leaves the bus apparently > happy, but Linux cannot access it. > > The current code is therefore pretty fragile. > > This fixes things by leaving the bus disabled unless we are actually > in a transaction. We enable the bus at the start of the transaction and > disable it at the end. That way we won't get interrupts and will not > lock up the bus. > > It might be possible to clear pending interrupts on start-up, but this > seems to be a more robust solution. We can't service interrupts when > we are not in a transaction, and anyway would rather not lock up the > bus while we try. > > Signed-off-by: Simon Glass > Cc: Grant Grundler > Signed-off-by: Naveen Krishna Chatradhi > --- > drivers/i2c/busses/i2c-s3c2410.c | 37 +++++++++++++++++++++++++++++++++---- > 1 file changed, 33 insertions(+), 4 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c > index e93e7d6..2fd346d 100644 > --- a/drivers/i2c/busses/i2c-s3c2410.c > +++ b/drivers/i2c/busses/i2c-s3c2410.c > @@ -186,6 +186,31 @@ static inline void s3c24xx_i2c_enable_irq(struct s3c24xx_i2c *i2c) > writel(tmp | S3C2410_IICCON_IRQEN, i2c->regs + S3C2410_IICCON); > } > > +/* > + * Disable the bus so that we won't get any interrupts from now on, or try > + * to drive any lines. This is the default state when we don't have > + * anything to send/receive. > + * > + * If there is an event on the bus, or we have a pre-existing event at > + * kernel boot time, we may not notice the event and the I2C controller > + * will lock the bus with the I2C clock line low indefinitely. > + */ > +static inline void s3c24xx_i2c_disable_bus(struct s3c24xx_i2c *i2c) > +{ > + unsigned long tmp; > + > + /* Stop driving the I2C pins */ > + tmp = readl(i2c->regs + S3C2410_IICSTAT); > + tmp &= ~S3C2410_IICSTAT_TXRXEN; > + writel(tmp, i2c->regs + S3C2410_IICSTAT); > + > + /* We don't expect any interrupts now, and don't want send acks */ > + tmp = readl(i2c->regs + S3C2410_IICCON); > + tmp &= ~(S3C2410_IICCON_IRQEN | S3C2410_IICCON_IRQPEND | > + S3C2410_IICCON_ACKEN); > + writel(tmp, i2c->regs + S3C2410_IICCON); > +} > + > > /* s3c24xx_i2c_message_start > * > @@ -646,7 +671,11 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c, > > s3c24xx_i2c_wait_idle(i2c); > > + s3c24xx_i2c_disable_bus(i2c); > + > out: > + i2c->state = STATE_IDLE; > + > return ret; > } > > @@ -912,7 +941,6 @@ static void s3c24xx_i2c_dt_gpio_free(struct s3c24xx_i2c *i2c) > > static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c) > { > - unsigned long iicon = S3C2410_IICCON_IRQEN | S3C2410_IICCON_ACKEN; > struct s3c2410_platform_i2c *pdata; > unsigned int freq; > > @@ -926,12 +954,12 @@ static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c) > > dev_info(i2c->dev, "slave address 0x%02x\n", pdata->slave_addr); > > - writel(iicon, i2c->regs + S3C2410_IICCON); > + writel(0, i2c->regs + S3C2410_IICCON); > + writel(0, i2c->regs + S3C2410_IICSTAT); > > /* we need to work out the divisors for the clock... */ > > if (s3c24xx_i2c_clockrate(i2c, &freq) != 0) { > - writel(0, i2c->regs + S3C2410_IICCON); > dev_err(i2c->dev, "cannot meet bus frequency required\n"); > return -EINVAL; > } > @@ -939,7 +967,8 @@ static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c) > /* todo - check that the i2c lines aren't being dragged anywhere */ > > dev_info(i2c->dev, "bus frequency set to %d KHz\n", freq); > - dev_dbg(i2c->dev, "S3C2410_IICCON=0x%02lx\n", iicon); > + dev_dbg(i2c->dev, "S3C2410_IICCON=0x%02x\n", > + readl(i2c->regs + S3C2410_IICCON)); > > return 0; > } > -- > 1.7.9.5 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/