From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2F37FC2BD09 for ; Mon, 24 Jun 2024 15:49:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=Z9kgIYkCaEISawG3z3/PKDsfUfni6CT+YfmQGd+f5vk=; b=DS4FQak9uJn8oaHLkvWK5Lt9S7 3foC5gz/KRbNVFZL9iV67NvFfiECXr85mUsKZFOGgDkCxqVfVwCK4ky2eSPMG8r2Hb+W9KXozIThp bHfuGsdHOC3WKfNS82MmeD9dI2lQNEIFM3MScpjDE6ESD/AVsVVRlpoOG+eNPlL6/viicUsFcBhrI xSd1IZs+E1FUZSzozk4EQ5PHMHs7kzbeXWSeua02PJE148gKB1jOXek7nSoM9HtNWZYgjzzSNorwa rnrF6JVUyKaKh3wPraRk7P7A37BglYmh7mkhg7rmfnDyVxdLabngpelU8LyIWop6474MFf4yOYhSi 8qSECUgQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sLlwm-0000000HNQu-3GS6; Mon, 24 Jun 2024 15:49:36 +0000 Received: from mail-wm1-x332.google.com ([2a00:1450:4864:20::332]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sLlwh-0000000HNQ8-3xh0 for linux-arm-kernel@lists.infradead.org; Mon, 24 Jun 2024 15:49:33 +0000 Received: by mail-wm1-x332.google.com with SMTP id 5b1f17b1804b1-4248e28de9eso11909375e9.2 for ; Mon, 24 Jun 2024 08:49:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1719244169; x=1719848969; darn=lists.infradead.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=Z9kgIYkCaEISawG3z3/PKDsfUfni6CT+YfmQGd+f5vk=; b=AQN4xPLL+GulVXiWU+fOdq9QJ/SfEEu0RNbkzKAkwjsIMj5Bk1qFQUVK+Bgzq2rH1O CHLMSL8HjaMamqkk4Mx97kOPQxrTHg2+z+/ZjvbWuab24WJNQ1sGPFt1/F0mWwjHAj6e 01fCC28hrRI03trqgZ+psDg9XPlM10V1T8AFE28GOhUZA+5qXwR/gYXlQ6xDKMIlVEJW sH0mldg9ilNexBwFBiAyhkv/BWsNgUTYTgqroHiXJ4KqtzmtbWaQyy6DuqRA43vcePK9 A2UhcXVvhbncFFvGOlnXo4xxkYEbxoAIhH7PJRhyzW6IzHsyoV8OPHe30GfpYMgaqxVk 0r+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1719244169; x=1719848969; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Z9kgIYkCaEISawG3z3/PKDsfUfni6CT+YfmQGd+f5vk=; b=d57hXS+tTqhLe8+HKf9n1FJ2mhKaKY9NQSPai+w1xZdpDRtJ0Pv/OPVAWyO+4MM7Pn 6LlSYI/kNHZ8xiHlE+mbIhN6t8jTPGIz5XtRIhPL2dXoLHQMBmrmFgJ9qAUlmKqGFP8I i9fp8Dr3+Mr0ysYsNHIdkPLnqbKny9kflA5bX1TxeF3/EJCyD523ZO8HXGlrg3hQztXU J+S1ZrzKAxHjukUDp0rf/By/K0X95iA5rF6cUrsYhwfQnFi9gKL/fYqWneliqFHFl4mT /sjIq1PwD1ESp2OcFioORwTvuxpB+rh0fuSM21fCE6pGXNeZnO31WjWjYAhNbaGgjbgB MLog== X-Forwarded-Encrypted: i=1; AJvYcCXIn3p7ctHXS55+qMnmeS1k86eIzd5T8STPpTRkChG806X6r4jjGmJiK1HxspC6nJfIMzFMimwAHujTJMUrbj70OLikjXkTmpnD01Tqjb+sHRElT+0= X-Gm-Message-State: AOJu0YwXXf54HezUL8MoDfOiZ1tOLBvkeWrmIkLQY8E5GbEp/fFq6mig f9Boq9DCoYTZ9kNMOo28ABUUVYOkJEjTyf/ASEUC/+JD+tFpbly0 X-Google-Smtp-Source: AGHT+IF2O0vTFTR2Jv5inHaCYhFCJMD7FD4fHIJxFEqeF2HsybT87gdE0Y0w/WzRojs+ABU4W/YZag== X-Received: by 2002:a05:600c:548b:b0:421:f04d:ebd2 with SMTP id 5b1f17b1804b1-4248cc349afmr33870795e9.22.1719244169043; Mon, 24 Jun 2024 08:49:29 -0700 (PDT) Received: from eichest-laptop ([2a02:168:af72:0:b172:75e:e42d:1a1d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4247d0be80dsm177295645e9.19.2024.06.24.08.49.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jun 2024 08:49:28 -0700 (PDT) Date: Mon, 24 Jun 2024 17:49:26 +0200 From: Stefan Eichenberger To: Oleksij Rempel Cc: kernel@pengutronix.de, andi.shyti@kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de, festevam@gmail.com, jic23@kernel.org, lars@metafoo.de, nuno.sa@analog.com, andriy.shevchenko@linux.intel.com, marcelo.schmitt@analog.com, gnstark@salutedevices.com, francesco.dolcini@toradex.com, wsa+renesas@sang-engineering.com, andrew@lunn.ch, linux-i2c@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, Stefan Eichenberger Subject: Re: [RFC PATCH] i2c: imx: avoid rescheduling when waiting for bus not busy Message-ID: References: <20240531142437.74831-1-eichest@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240624_084932_008481_F1F4E648 X-CRM114-Status: GOOD ( 61.46 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Oleksij, On Sat, Jun 22, 2024 at 07:02:39AM +0200, Oleksij Rempel wrote: > Hi Stefan, > > On Fri, Jun 21, 2024 at 05:22:46PM +0200, Stefan Eichenberger wrote: > > Hi Andi, Andrew, Wolfram, Oleksij, > > > > After some internal discussion we still have some questions which are > > blocking us from solving the issue. > > > > On Fri, May 31, 2024 at 04:24:37PM +0200, Stefan Eichenberger wrote: > > > From: Stefan Eichenberger > > > > > > On our i.MX8M Mini based module we have an ADS1015 I2C ADC connected to > > > the I2C bus. The ADS1015 I2C ADC will timeout after 25ms when the I2C > > > bus is idle. The imx i2c driver will call schedule when waiting for the > > > bus to become idle after switching to master mode. When the i2c > > > controller switches to master mode it pulls SCL and SDA low, if the > > > ADS1015 I2C ADC sees this for more than 25 ms without seeing SCL > > > clocking, it will timeout and ignore all signals until the next start > > > condition occurs (SCL and SDA low). This can occur when the system load > > > is high and schedule returns after more than 25 ms. > > > > > > This rfc tries to solve the problem by using a udelay for the first 10 > > > ms before calling schedule. This reduces the chance that we will > > > reschedule. However, it is still theoretically possible for the problem > > > to occur. To properly solve the problem, we would also need to disable > > > interrupts during the transfer. > > > > > > After some internal discussion, we see three possible solutions: > > > 1. Use udelay as shown in this rfc and also disable the interrupts > > > during the transfer. This would solve the problem but disable the > > > interrupts. Also, we would have to re-enable the interrupts if the > > > timeout is longer than 1ms (TBD). > > > 2. We use a retry mechanism in the ti-ads1015 driver. When we see a > > > timeout, we try again. > > > 3. We use the suggested solution and accept that there is an edge case > > > where the timeout can happen. > > > > > > There may be a better way to do this, which is why this is an RFC. > > > > > > Signed-off-by: Stefan Eichenberger > > > --- > > > drivers/i2c/busses/i2c-imx.c | 14 +++++++++++--- > > > 1 file changed, 11 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c > > > index 3842e527116b7..179f8367490a5 100644 > > > --- a/drivers/i2c/busses/i2c-imx.c > > > +++ b/drivers/i2c/busses/i2c-imx.c > > > @@ -503,10 +503,18 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy, bool a > > > "<%s> I2C bus is busy\n", __func__); > > > return -ETIMEDOUT; > > > } > > > - if (atomic) > > > + if (atomic) { > > > udelay(100); > > > - else > > > - schedule(); > > > + } else { > > > + /* > > > + * Avoid rescheduling in the first 10 ms to avoid > > > + * timeouts for SMBus like devices > > > + */ > > > + if (time_before(jiffies, orig_jiffies + msecs_to_jiffies(10))) > > > + udelay(10); > > > + else > > > + schedule(); > > > + } > > > } > > > > > > return 0; > > > -- > > > 2.40.1 > > > > If we want to be sure that the ADS1015 I2C ADC will never timeout, we > > would have to add a patch to disable preemption during transmission. > > This would look like this: > > > > @@ -1244,6 +1248,12 @@ static int i2c_imx_xfer_common(struct i2c_adapter *adapter, > > bool is_lastmsg = false; > > struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter); > > > > + /* If we are in SMBus mode we need to do the transfer atomically */ > > + if (i2c_imx->smbus_mode) { > > + preempt_disable(); > > + atomic = true; > > + } > > + > > /* Start I2C transfer */ > > result = i2c_imx_start(i2c_imx, atomic); > > if (result) { > > @@ -1320,6 +1330,9 @@ static int i2c_imx_xfer_common(struct i2c_adapter *adapter, > > if (i2c_imx->slave) > > i2c_imx_slave_init(i2c_imx); > > > > + if (i2c_imx->smbus_mode) > > + preempt_enable(); > > + > > return (result < 0) ? result : num; > > } > > > > However, we are aware that disabling preemption is not a good idea. So > > we were discussing how this is normally handled with SMBus devices? Is > > it just expected that SMBus devices will timeout in rare cases? > > > > For our use case, the problem would be solved if we could get rid of the > > schedule call and replace it with a udelay. It seems that the i.MX8M > > Mini I2C controller needs a few ms to clear the IBB flag. In the > > reference manual, they write: > > > I2C bus busy bit. Indicates the status of the bus. NOTE: When I2C is > > > enabled (I2C_I2CR[IEN] = 1), it continuously polls the bus data (SDA) > > > and clock (SCL) signals to determine a Start or Stop condition. Bus is > > > idle. If a Stop signal is detected, IBB is cleared. Bus is busy. When > > > Start is detected, IBB is set. > > Unfortunately, it is not clear how often they poll. In our tests the > > issue disappeard when we used udelay instead of usleep or schedule for > > the first 10 ms. > > I'm not really happy with this variant. It can be acceptable in some > use cases, but may have not pleasant side effects on other. Since this > is still valid case, I would prefer to have a UAPI to enable polling > mode as optional optimization with a warning that it may affect latency > on other corner of the system. > > > Since we know we don't have a multi-master configuration, another way > > would be to not test for IBB and just start the transfer. We saw that > > other drivers use the multi-master device tree property to determine if > > multi-master is supported. Here another quote from the reference manual: > > > On a multimaster bus system, the busy bus (I2C_I2SR[IBB]) must be > > > tested to determine whether the serial bus is free. > > We assume this means it is not necessary to test for IBB if we know we > > are in a single-master configuration. > > I interpret this part of documentation in the same way, so it will be > great if you can implement this option. Perfect thanks a lot for the feedback. I will try to implement this option and run some tests to make sure it will not break anything. Best regards, Stefan