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Mon, 02 Nov 2026 20:13:54 +0530 Message-ID: <54497841-56cd-4a41-9f42-e4e6f9c17b51@roeck-us.net> Date: Mon, 2 Nov 2026 06:43:53 -0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 5/7] hwmon: sy7636a: read the temperature only while the rails are on To: Andreas Kemnade Cc: Pablo Mazzini , Alistair Francis , linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261101223125.302001-1-pmazzini@gmail.com> <20261101223125.302001-6-pmazzini@gmail.com> <2c48d47a-85f5-48e8-a675-239b033eb0ce@roeck-us.net> <20261102112522.76e02b83@kemnade.info> Content-Language: en-US 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 CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAmgrMyQFCSbODQkACgkQyx8mb86fmYGcWRAA oRwrk7V8fULqnGGpBIjp7pvR187Yzx+lhMGUHuM5H56TFEqeVwCMLWB2x1YRolYbY4MEFlQg VUFcfeW0OknSr1s6wtrtQm0gdkolM8OcCL9ptTHOg1mmXa4YpW8QJiL0AVtbpE9BroeWGl9v 2TGILPm9mVp+GmMQgkNeCS7Jonq5f5pDUGumAMguWzMFEg+Imt9wr2YA7aGen7KPSqJeQPpj onPKhu7O/KJKkuC50ylxizHzmGx+IUSmOZxN950pZUFvVZH9CwhAAl+NYUtcF5ry/uSYG2U7 DCvpzqOryJRemKN63qt1bjF6cltsXwxjKOw6CvdjJYA3n6xCWLuJ6yk6CAy1Ukh545NhgBAs rGGVkl6TUBi0ixL3EF3RWLa9IMDcHN32r7OBhw6vbul8HqyTFZWY2ksTvlTl+qG3zV6AJuzT WdXmbcKN+TdhO5XlxVlbZoCm7ViBj1+PvIFQZCnLAhqSd/DJlhaq8fFXx1dCUPgQDcD+wo65 qulV/NijfU8bzFfEPgYP/3LP+BSAyFs33y/mdP8kbMxSCjnLEhimQMrSSo/To1Gxp5C97fw5 3m1CaMILGKCmfI1B8iA8zd8ib7t1Rg0qCwcAnvsM36SkrID32GfFbv873bNskJCHAISK3Xkz qo7IYZmjk/IJGbsiGzxUhvicwkgKE9r7a1rOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 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 JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAmgrMyQFCSbODQkACgkQyx8mb86fmYHlgg/9 H5JeDmB4jsreE9Bn621wZk7NMzxy9STxiVKSh8Mq4pb+IDu1RU2iLyetCY1TiJlcxnE362kj njrfAdqyPteHM+LU59NtEbGwrfcXdQoh4XdMuPA5ADetPLma3YiRa3VsVkLwpnR7ilgwQw6u dycEaOxQ7LUXCs0JaGVVP25Z2hMkHBwx6BlW6EZLNgzGI2rswSZ7SKcsBd1IRHVf0miwIFYy j/UEfAFNW+tbtKPNn3xZTLs3quQN7GdYLh+J0XxITpBZaFOpwEKV+VS36pSLnNl0T5wm0E/y scPJ0OVY7ly5Vm1nnoH4licaU5Y1nSkFR/j2douI5P7Cj687WuNMC6CcFd6j72kRfxklOqXw zvy+2NEcXyziiLXp84130yxAKXfluax9sZhhrhKT6VrD45S6N3HxJpXQ/RY/EX35neH2/F7B RgSloce2+zWfpELyS1qRkCUTt1tlGV2p+y2BPfXzrHn2vxvbhEn1QpQ6t+85FKN8YEhJEygJ F0WaMvQMNrk9UAUziVcUkLU52NS9SXqpVg8vgrO0JKx97IXFPcNh0DWsSj/0Y8HO/RDkGXYn FDMj7fZSPKyPQPmEHg+W/KzxSSfdgWIHF2QaQ0b2q1wOSec4Rti52ohmNSY+KNIW/zODhugJ np3900V20aS7eD9K8GTU0TGC1pyz6IVJwIE= In-Reply-To: <20261102112522.76e02b83@kemnade.info> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-BWhitelist: no X-Source-IP: 108.223.40.66 X-Source-L: No X-Exim-ID: 1xNtGM-00000003eMA-1WwC X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 108-223-40-66.lightspeed.sntcca.sbcglobal.net [108.223.40.66]:57474 X-Source-Auth: guenter@roeck-us.net X-Email-Count: 6 X-Org: HG=direseller_whb_net_legacy;ORG=directi; X-Source-Cap: cm9lY2s7YWN0aXZzdG07YmgtMjUud2ViaG9zdGJveC5uZXQ= X-Local-Domain: yes X-CMAE-Envelope: MS4xfNFxJot6Q0zU5zNV8aw0IFPVqMnLcuAOE2EMNfLaWHYVKawaMXz8+E5qcOrcQQI3xN4z62+ujmoCH7onAXscDENfwAJefTULWqph5g61k92flamRGT9U 1q9uTMtAxEMzyxsZJwiE4TDTA43cedy6yy+pg8ujoEBoJ62lL9DJtaVjoPm84dDnYvN0KBBRyh7BhsvuNjcPjveMkhg7G+21yToYxcPMUX23/wLPWvPwdwZD On 11/2/26 02:25, Andreas Kemnade wrote: > On Sun, 1 Nov 2026 19:35:16 -0800 > Guenter Roeck wrote: > >> On 11/1/26 14:31, Pablo Mazzini wrote: >>> The driver enables VCOM at probe, which keeps the panel's high voltage >>> rails on for good, and gets a dummy regulator if it probes before the >>> regulator exists. Read the temperature only while the rails are on, when >>> the chip samples it, and return -ENODATA otherwise. Read power good with >>> it in one transfer, so the value can not be from before the first sample >>> or after the rails went off. Register it under the chip name, as the >>> TPS65185 and FP9931 drivers do. >>> >>> Signed-off-by: Pablo Mazzini >>> --- >>> drivers/hwmon/sy7636a-hwmon.c | 25 ++++++++++++++----------- >>> 1 file changed, 14 insertions(+), 11 deletions(-) >>> >>> diff --git a/drivers/hwmon/sy7636a-hwmon.c b/drivers/hwmon/sy7636a-hwmon.c >>> index f01f368d68e5..475aff997c2d 100644 >>> --- a/drivers/hwmon/sy7636a-hwmon.c >>> +++ b/drivers/hwmon/sy7636a-hwmon.c >>> @@ -14,7 +14,6 @@ >>> #include >>> #include >>> #include >>> -#include >> >>> #include >>> >>> @@ -22,14 +21,22 @@ static int sy7636a_read(struct device *dev, enum hwmon_sensor_types type, >>> u32 attr, int channel, long *temp) >>> { >>> struct regmap *regmap = dev_get_drvdata(dev); >>> - int ret, reg_val; >>> - >>> - ret = regmap_read(regmap, >>> - SY7636A_REG_TERMISTOR_READOUT, ®_val); >>> + u8 buf[2]; >>> + int ret; >>> + >>> + /* >>> + * Read power good and the thermistor in one transfer: the thermistor is >>> + * only sampled while the rails are on, and power good comes after the >>> + * first sample >>> + */ >>> + ret = regmap_bulk_read(regmap, SY7636A_REG_FAULT_FLAG, buf, sizeof(buf)); >>> if (ret) >>> return ret; >>> >>> - *temp = (s8)reg_val * 1000; >>> + if (!(buf[0] & SY7636A_FAULT_FLAG_PG)) >>> + return -ENODATA; >>> + >> >> I had a look at the datasheet. It does not say anything about the >> temperature not being measured when PG is not set. >> > That is what I read from there, too. But the PG bit will only > be set if the On/Off bit is also set. > >> The datasheet does suggest that temperatures are only measured >> if bit 7 of the operation mode register is set, but that is >> different from the "power good" bit in the fault register. >> > I can confirm from tests that temperature reads zero if regulator > was not yet powered on. > > I read the datasheet in that way so things happen it that order: > > 1. on bit is set > 2. ramping up voltages start / temperature sampling starts. > 3. after some time (sampling time + conversion time (ADC_SPL+ADC_DEL)?), > the first sample is ready and the temperature can be read. > 4. after some more time voltage lines stabilize > 5. after 1.5 ms PG is asserted > >> So why the association with the PG bit and not with the On/Off bit >> of the operation mode register ? That warrants some more explanation. > > That should definitively be commented in the code. I have pointed out > races earlier. This has of course the drawback that it limits the time > frame in which reads are possible a bit. I doubt it is worth dealing with > synchronisation code to use that on/off bit (although posssible). > As mentioned in the other mail, downside is that the temperature will not be reported if EN=1 and PG=0 (for whatever reason), even though the temperature may be available. At the very least the reason for accepting this limitation will need to be explained in the driver. Guenter