Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751739AbaBGIua (ORCPT ); Fri, 7 Feb 2014 03:50:30 -0500 Received: from mail-pb0-f45.google.com ([209.85.160.45]:57818 "EHLO mail-pb0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751134AbaBGIu2 (ORCPT ); Fri, 7 Feb 2014 03:50:28 -0500 MIME-Version: 1.0 In-Reply-To: <20130124122036.GF12933@pengutronix.de> References: <1354165536-18529-1-git-send-email-ch.naveen@samsung.com> <1354165536-18529-2-git-send-email-ch.naveen@samsung.com> <20130124122036.GF12933@pengutronix.de> From: Naveen Krishna Ch Date: Fri, 7 Feb 2014 14:20:07 +0530 Message-ID: Subject: Re: [PATCH 1/2] i2c-s3c2410: Leave the bus disabled unless it is in use To: Wolfram Sang Cc: Naveen Krishna Chatradhi , linux-arm-kernel@lists.infradead.org, "linux-samsung-soc@vger.kernel.org" , linux-i2c@vger.kernel.org, Naveen Krishna , sjg@chromium.org, grundler@chromium.org, 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 Hello Wolfram, Sorry for a replying after really long time. On 24 January 2013 17:50, Wolfram Sang wrote: > On Thu, Nov 29, 2012 at 10:35:34AM +0530, 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 > > So, I assume this patch is still needed despite the ongoing discussion > about arbitration? Yes, this is an i2c crontroller fix. > >> --- >> 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 > > Otherwise, if... > >> + * 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; >> + > > Why is the state change after the label? As the interrupts are enabled in the beginning of this function. and interrupts in STATE_IDLE needs handling in a different way. This was added with the intention the irq routine will handle the cases > >> 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)); >> > > Regards, > > Wolfram Will re-base and post the patch.. > > -- > Pengutronix e.K. | Wolfram Sang | > Industrial Linux Solutions | http://www.pengutronix.de/ | -- Shine bright, (: Nav :) -- 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/