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([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b439ed0f6sm4122463b3a.218.2024.07.10.12.16.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jul 2024 12:16:57 -0700 (PDT) Sender: Guenter Roeck Message-ID: <201dec9d-bba0-477b-bbb2-c17aa37b944a@roeck-us.net> Date: Wed, 10 Jul 2024 12:16:55 -0700 Precedence: bulk X-Mailing-List: linux-i2c@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] hwmon: (pmbus/ltc4286) Improve device matching To: =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= Cc: Delphine CC Chiu , Jean Delvare , linux-i2c@vger.kernel.org, linux-hwmon@vger.kernel.org References: <3jyzvldeh32cwjmvcuhazmz2jzuqjcbnza4yajnn2ky7mcby37@aswnxwoe6whu> 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 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= In-Reply-To: <3jyzvldeh32cwjmvcuhazmz2jzuqjcbnza4yajnn2ky7mcby37@aswnxwoe6whu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/10/24 08:48, Uwe Kleine-König wrote: > Hello Guenter, > > On Wed, Jul 10, 2024 at 07:09:28AM -0700, Guenter Roeck wrote: >> On 7/10/24 01:35, Uwe Kleine-König wrote: >>> The devices supported by this driver report the model name in their >>> register space. The way this is evaluated allows longer strings than the >>> driver's model list. Document this behaviour in a code comment to lessen >>> the surprise for the next reader. >>> >>> Additionally emit the reported model name in case of a mismatch. >>> >>> Signed-off-by: Uwe Kleine-König >>> --- >>> drivers/hwmon/pmbus/ltc4286.c | 12 +++++++++--- >>> 1 file changed, 9 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/hwmon/pmbus/ltc4286.c b/drivers/hwmon/pmbus/ltc4286.c >>> index 9e7ceeb7e789..2e5532300eff 100644 >>> --- a/drivers/hwmon/pmbus/ltc4286.c >>> +++ b/drivers/hwmon/pmbus/ltc4286.c >>> @@ -95,13 +95,19 @@ static int ltc4286_probe(struct i2c_client *client) >>> "Failed to read manufacturer model\n"); >>> } >>> - for (mid = ltc4286_id; mid->name[0]; mid++) { >>> + for (mid = ltc4286_id; mid->name[0]; mid++) >>> + /* >>> + * Note that by limiting the comparison to strlen(mid->name) >>> + * chars, the device reporting "lTc4286chocolade" is accepted, >>> + * too. >>> + */ >> >> This is misleading; the desired match is LTC4286 and all its variants (LTC4286[A-Z] and >> whatever else the vendor can come up with), i.e., it is supposed to include all device >> variants, and ignoring case since it is irrelevant. Referring to the odd string just >> makes that look unnecessarily bad. I am not going to apply this patch, sorry. > > You're quite an optimist, expecting "whatever the vendor can come up > with" but nothing bad :-) > "optimist" is relative. A perfectly valid alternative would be to _not_ do any testing at all. After all, this is not a detect function, this is the probe function, which should only be called _after_ the chip has been identified. Since the model number is not used for anything but extra validation, one might as well argue that the validation is unnecessary and can or should be dropped to reduce boot time. Of course, given the vagueness of the PMBus specification, that might result in fatal consequences if the wrong chip is instantiated, so I think that validation does make sense, and I suggest to add it for all PMBus drivers. However, one can overdo it (and not all drivers do it). > Anyhow, what about updating the comment to read: > > Note that by limiting the comparison to strlen(mid->name) chars, > matching for devices that report their model with a variant > suffix is supported. > > While looking at the code again, I spotted a (theoretic) bug: Given that > block_buffer isn't initialized at function entry, it might well contain > "LTC4286something" (which might even be realistic if the driver just > probed on a different bus?). Now if i2c_smbus_read_block_data(... > PMBUS_MFR_MODEL, ...) returned something between 0 and 6, we're looking > at bytes that didn't come from the block read. > Yes, I would agree that a check ensuring that ret >= 7 would make sense. Thanks, Guenter