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Mon, 09 Nov 2020 06:42:47 -0800 (PST) Sender: Guenter Roeck Subject: Re: [PATCH 3/3] hwmon: (ltc2945): add support for sense resistor To: Alexandru Ardelean Cc: Alexandru Ardelean , linux-hwmon@vger.kernel.org, LKML , jdelvare@suse.com, Mark.Thoren@analog.com References: <20201106101825.30960-1-alexandru.ardelean@analog.com> <20201106101825.30960-3-alexandru.ardelean@analog.com> <20201106131727.GD14837@roeck-us.net> 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: <11250d2d-c8ec-a1dc-2f80-edc531160d3e@roeck-us.net> Date: Mon, 9 Nov 2020 06:42:45 -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: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/8/20 10:41 PM, Alexandru Ardelean wrote: > On Fri, Nov 6, 2020 at 3:17 PM Guenter Roeck wrote: >> >> On Fri, Nov 06, 2020 at 12:18:25PM +0200, Alexandru Ardelean wrote: >>> The sense resistor is a parameter of the board. It should be configured in >>> the driver via a device-tree / ACPI property, so that the proper current >>> measurements can be done in the driver. >>> >>> It shouldn't be necessary that userspace need to know about the value of >>> the resistor. It makes things a bit harder to make the application code >>> portable from one board to another. >>> >>> This change implements support for the sense resistor to be configured from >>> DT/ACPI and used in current calculations. >>> >> >> This will require a matching deevicetree document. > > Ack > Will create a dt binding schema doc. > Are you fine with being added as maintainer in the DT doc? > Seeing as you are the original author of the driver. > Sure. Guenter >> >>> Signed-off-by: Alexandru Ardelean >>> --- >>> drivers/hwmon/ltc2945.c | 48 ++++++++++++++++++----------------------- >>> 1 file changed, 21 insertions(+), 27 deletions(-) >>> >>> diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c >>> index 75d997d31e01..500401a82c49 100644 >>> --- a/drivers/hwmon/ltc2945.c >>> +++ b/drivers/hwmon/ltc2945.c >>> @@ -61,9 +61,11 @@ >>> /** >>> * struct ltc2945_state - driver instance specific data >>> * @regmap regmap object to access device registers >>> + * @r_sense_uohm current sense resistor value >>> */ >>> struct ltc2945_state { >>> struct regmap *regmap; >>> + u32 r_sense_uohm; >>> }; >>> >>> static inline bool is_power_reg(u8 reg) >>> @@ -101,9 +103,8 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) >>> case LTC2945_MAX_POWER_THRES_H: >>> case LTC2945_MIN_POWER_THRES_H: >>> /* >>> - * Convert to uW by assuming current is measured with >>> - * an 1mOhm sense resistor, similar to current >>> - * measurements. >>> + * Convert to uW by and scale it with the configured >>> + * sense resistor, similar to current measurements. >>> * Control register bit 0 selects if voltage at SENSE+/VDD >>> * or voltage at ADIN is used to measure power. >>> */ >>> @@ -112,10 +113,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) >>> return ret; >>> if (control & CONTROL_MULT_SELECT) { >>> /* 25 mV * 25 uV = 0.625 uV resolution. */ >>> - val *= 625LL; >>> + val = DIV_ROUND_CLOSEST_ULL(val * 625LL * 1000, st->r_sense_uohm); >>> } else { >>> /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ >>> - val = (val * 25LL) >> 1; >>> + val = DIV_ROUND_CLOSEST_ULL(val * 25LL * 1000, st->r_sense_uohm) >> 1; >>> } >>> break; >>> case LTC2945_VIN_H: >>> @@ -140,13 +141,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg) >>> case LTC2945_MAX_SENSE_THRES_H: >>> case LTC2945_MIN_SENSE_THRES_H: >>> /* >>> - * 25 uV resolution. Convert to current as measured with >>> - * an 1 mOhm sense resistor, in mA. If a different sense >>> - * resistor is installed, calculate the actual current by >>> - * dividing the reported current by the sense resistor value >>> - * in mOhm. >>> + * 25 uV resolution. Convert to current and scale it >>> + * with the value of the sense resistor. >>> */ >>> - val *= 25; >>> + val = DIV_ROUND_CLOSEST_ULL(val * 25 * 1000, st->r_sense_uohm); >>> break; >>> default: >>> return -EINVAL; >>> @@ -169,9 +167,8 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, >>> case LTC2945_MAX_POWER_THRES_H: >>> case LTC2945_MIN_POWER_THRES_H: >>> /* >>> - * Convert to register value by assuming current is measured >>> - * with an 1mOhm sense resistor, similar to current >>> - * measurements. >>> + * Convert to register value, scale it with the configured sense >>> + * resistor value, similar to current measurements. >>> * Control register bit 0 selects if voltage at SENSE+/VDD >>> * or voltage at ADIN is used to measure power, which in turn >>> * determines register calculations. >>> @@ -181,14 +178,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, >>> return ret; >>> if (control & CONTROL_MULT_SELECT) { >>> /* 25 mV * 25 uV = 0.625 uV resolution. */ >>> - val = DIV_ROUND_CLOSEST_ULL(val, 625); >>> + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 625 * st->r_sense_uohm); >>> } else { >>> - /* >>> - * 0.5 mV * 25 uV = 0.0125 uV resolution. >>> - * Divide first to avoid overflow; >>> - * accept loss of accuracy. >>> - */ >>> - val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2; >>> + /* 0.5 mV * 25 uV = 0.0125 uV resolution. */ >>> + val = DIV_ROUND_CLOSEST_ULL(val * 2 * 1000, 25 * st->r_sense_uohm); >>> } >>> break; >>> case LTC2945_VIN_H: >>> @@ -213,13 +206,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg, >>> case LTC2945_MAX_SENSE_THRES_H: >>> case LTC2945_MIN_SENSE_THRES_H: >>> /* >>> - * 25 uV resolution. Convert to current as measured with >>> - * an 1 mOhm sense resistor, in mA. If a different sense >>> - * resistor is installed, calculate the actual current by >>> - * dividing the reported current by the sense resistor value >>> - * in mOhm. >>> + * 25 uV resolution. Convert to current and scale it >>> + * with the value of the sense resistor, in mA. >>> */ >>> - val = DIV_ROUND_CLOSEST_ULL(val, 25); >>> + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 25 * st->r_sense_uohm); >>> break; >>> default: >>> return -EINVAL; >>> @@ -475,6 +465,10 @@ static int ltc2945_probe(struct i2c_client *client) >>> return PTR_ERR(regmap); >>> } >>> >>> + if (device_property_read_u32(dev, "shunt-resistor-micro-ohms", >>> + &st->r_sense_uohm)) >>> + st->r_sense_uohm = 1000; >>> + >> >> Devicetree could set shunt-resistor-micro-ohms to 0, which would result >> in divide by 0 errors. > > Ack > Will do a check for this. > >> >> Guenter >> >>> st->regmap = regmap; >>> >>> /* Clear faults */ >>> -- >>> 2.27.0 >>>