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Wed, 10 Mar 2021 23:41:35 -0800 (PST) Sender: Guenter Roeck Subject: Re: Errant readings on LM81 with T2080 SoC To: Chris Packham , "jdelvare@suse.com" Cc: "linux-hwmon@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-i2c@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" References: <8e0a88ba-01e9-9bc1-c78b-20f26ce27d12@alliedtelesis.co.nz> <96d660bc-17ab-4e0e-9a94-bce1737a8da1@roeck-us.net> <4a1b1494-df96-2d8c-9323-beb2c2ba706b@alliedtelesis.co.nz> <5709f180-04b5-09b2-e1c4-53eb5c9345d8@roeck-us.net> <1aa0dc23-0706-5902-2f46-0767de0e3ad6@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: Date: Wed, 10 Mar 2021 23:41:33 -0800 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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On 3/10/21 1:48 PM, Chris Packham wrote: > > On 10/03/21 6:06 pm, Guenter Roeck wrote: >> On 3/9/21 6:19 PM, Chris Packham wrote: >>> On 9/03/21 9:27 am, Chris Packham wrote: >>>> On 8/03/21 5:59 pm, Guenter Roeck wrote: >>>>> Other than that, the only other real idea I have would be to monitor >>>>> the i2c bus. >>>> I am in the fortunate position of being able to go into the office and >>>> even happen to have the expensive scope at the moment. Now I just need >>>> to find a tame HW engineer so I don't burn myself trying to attach the >>>> probes. >>> One thing I see on the scope is that when there is a CPU load there >>> appears to be some clock stretching going on (SCL is held low some >>> times). I don't see it without the CPU load. It's hard to correlate a >>> clock stretching event with a bad read or error but it is one area where >>> the SMBUS spec has a maximum that might cause the device to give up waiting. >>> >> Do you have CONFIG_PREEMPT enabled in your kernel ? But even without >> that it is possible that the hot loops at the beginning and end of >> each operation mess up the driver and cause it to sleep longer >> than intended. Did you try usleep_range() ? > > I've been running with and without CONFIG_PREEMPT. The failures happen > with both. > > I did try usleep_range() and still saw failures. > 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. I wonder if there are some timing differences before the clock stretching happens. Anyway, I just sent a set of three patches to the list; maybe you can give it a try. The patches convert the driver to the with_info API and drop local caching. The code is module tested with the register dumps I have available for adm9240 and lm81, but it would be great to get test coverage on real hardware. I don't really expect it to solve your problem, but it does reduce and modify the load on the chip (because registers are no longer read in bursts), so it may have some positive impact. >> On a side note, can you send me a register dump for the lm81 ? >> It would be useful for my module test code. > > Here you go this is from a largely unconfigured LM81 > Thanks, that helped a lot! 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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" , "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 3/10/21 1:48 PM, Chris Packham wrote: > > On 10/03/21 6:06 pm, Guenter Roeck wrote: >> On 3/9/21 6:19 PM, Chris Packham wrote: >>> On 9/03/21 9:27 am, Chris Packham wrote: >>>> On 8/03/21 5:59 pm, Guenter Roeck wrote: >>>>> Other than that, the only other real idea I have would be to monitor >>>>> the i2c bus. >>>> I am in the fortunate position of being able to go into the office and >>>> even happen to have the expensive scope at the moment. Now I just need >>>> to find a tame HW engineer so I don't burn myself trying to attach the >>>> probes. >>> One thing I see on the scope is that when there is a CPU load there >>> appears to be some clock stretching going on (SCL is held low some >>> times). I don't see it without the CPU load. It's hard to correlate a >>> clock stretching event with a bad read or error but it is one area where >>> the SMBUS spec has a maximum that might cause the device to give up waiting. >>> >> Do you have CONFIG_PREEMPT enabled in your kernel ? But even without >> that it is possible that the hot loops at the beginning and end of >> each operation mess up the driver and cause it to sleep longer >> than intended. Did you try usleep_range() ? > > I've been running with and without CONFIG_PREEMPT. The failures happen > with both. > > I did try usleep_range() and still saw failures. > 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. I wonder if there are some timing differences before the clock stretching happens. Anyway, I just sent a set of three patches to the list; maybe you can give it a try. The patches convert the driver to the with_info API and drop local caching. The code is module tested with the register dumps I have available for adm9240 and lm81, but it would be great to get test coverage on real hardware. I don't really expect it to solve your problem, but it does reduce and modify the load on the chip (because registers are no longer read in bursts), so it may have some positive impact. >> On a side note, can you send me a register dump for the lm81 ? >> It would be useful for my module test code. > > Here you go this is from a largely unconfigured LM81 > Thanks, that helped a lot! Guenter