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Wed, 17 Mar 2021 21:02:02 -0700 (PDT) Sender: Guenter Roeck Subject: Re: Errant readings on LM81 with T2080 SoC To: Chris Packham , Wolfram Sang Cc: "jdelvare@suse.com" , "linux-hwmon@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-i2c@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" References: <20210311081842.GA1070@ninjato> <94dfa9dc-a80c-98ba-4169-44cce3d810f7@alliedtelesis.co.nz> <725c5e51-65df-e17d-e2da-0982efacf2d2@roeck-us.net> <9c912424-2cc9-8753-1352-1a5c27722cd2@alliedtelesis.co.nz> From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= Message-ID: <8e516ef6-340e-a873-68a9-71a10008f32c@roeck-us.net> Date: Wed, 17 Mar 2021 21:02:00 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <9c912424-2cc9-8753-1352-1a5c27722cd2@alliedtelesis.co.nz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On 3/17/21 8:46 PM, Chris Packham wrote: > > On 12/03/21 10:34 am, Guenter Roeck wrote: >> On 3/11/21 1:17 PM, Chris Packham wrote: >>> On 11/03/21 9:18 pm, Wolfram Sang wrote: >>>>> Bummer. What is really weird is that you see clock stretching under >>>>> CPU load. Normally clock stretching is triggered by the device, not >>>>> by the host. >>>> One example: Some hosts need an interrupt per byte to know if they >>>> should send ACK or NACK. If that interrupt is delayed, they stretch the >>>> clock. >>>> >>> It feels like something like that is happening. Looking at the T2080 >>> Reference manual there is an interesting timing diagram (Figure 14-2 if >>> someone feels like looking it up). It shows SCL low between the ACK for >>> the address and the data byte. I think if we're delayed in sending the >>> next byte we could violate Ttimeout or Tlow:mext from the SMBUS spec. >>> >> I think that really leaves you only two options that I can see: >> Rework the driver to handle critical actions (such as setting TXAK, >> and everything else that might result in clock stretching) in the >> interrupt handler, or rework the driver to handle everything in >> a high priority kernel thread. > I've made some reasonable progress on making i2c-mpc more interrupt > driven. Assuming it works out for my use-case is there an opinion on > making interrupt support mandatory? Looking at all the in-tree dts files > that use one of the compatible strings from i2c-mpc.c they all have > interrupt properties so in theory nothing is using the polling mode. But > there may be some out-of-tree boards or boards using an old dtb that > would be affected? > The polling code is from pre-git times. Like 2005 and earlier. I'd say it is about time to get rid of it. Any out-of-tree users had more than 15 years to upstream their code, after all. 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <9c912424-2cc9-8753-1352-1a5c27722cd2@alliedtelesis.co.nz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-hwmon@vger.kernel.org" , "jdelvare@suse.com" , "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" , "linux-i2c@vger.kernel.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 3/17/21 8:46 PM, Chris Packham wrote: > > On 12/03/21 10:34 am, Guenter Roeck wrote: >> On 3/11/21 1:17 PM, Chris Packham wrote: >>> On 11/03/21 9:18 pm, Wolfram Sang wrote: >>>>> Bummer. What is really weird is that you see clock stretching under >>>>> CPU load. Normally clock stretching is triggered by the device, not >>>>> by the host. >>>> One example: Some hosts need an interrupt per byte to know if they >>>> should send ACK or NACK. If that interrupt is delayed, they stretch the >>>> clock. >>>> >>> It feels like something like that is happening. Looking at the T2080 >>> Reference manual there is an interesting timing diagram (Figure 14-2 if >>> someone feels like looking it up). It shows SCL low between the ACK for >>> the address and the data byte. I think if we're delayed in sending the >>> next byte we could violate Ttimeout or Tlow:mext from the SMBUS spec. >>> >> I think that really leaves you only two options that I can see: >> Rework the driver to handle critical actions (such as setting TXAK, >> and everything else that might result in clock stretching) in the >> interrupt handler, or rework the driver to handle everything in >> a high priority kernel thread. > I've made some reasonable progress on making i2c-mpc more interrupt > driven. Assuming it works out for my use-case is there an opinion on > making interrupt support mandatory? Looking at all the in-tree dts files > that use one of the compatible strings from i2c-mpc.c they all have > interrupt properties so in theory nothing is using the polling mode. But > there may be some out-of-tree boards or boards using an old dtb that > would be affected? > The polling code is from pre-git times. Like 2005 and earlier. I'd say it is about time to get rid of it. Any out-of-tree users had more than 15 years to upstream their code, after all. Guenter