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[176.7.58.112]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499d5d72d36sm23411535e9.3.2026.08.25.06.17.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Aug 2026 06:17:31 -0700 (PDT) Message-ID: <9e7edec5-578d-48e0-b253-e50cf848236e@gmail.com> Date: Tue, 25 Aug 2026 15:17:14 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 08/14] iio: adc: ad7768: Add per-channel conversion delay To: Andy Shevchenko , Janani Sunil Cc: =?UTF-8?Q?Nuno_S=C3=A1?= , Michael Hennerich , Jonathan Cameron , David Lechner , Andy Shevchenko , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Olivier Moysan , Philipp Zabel , Linus Walleij , Bartosz Golaszewski , Jonathan Corbet , Shuah Khan , Michael Walle , linux@analog.com, linux-iio@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-gpio@vger.kernel.org, linux-doc@vger.kernel.org, =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= References: <20260821-ad7768-driver-v4-0-bb8fbd06d4eb@analog.com> <20260821-ad7768-driver-v4-8-bb8fbd06d4eb@analog.com> Content-Language: en-US From: Janani Sunil In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/24/26 09:10, Andy Shevchenko wrote: > On Fri, Aug 21, 2026 at 04:07:01PM +0200, Janani Sunil wrote: >> Expose the per-channel synchronization phase offset through the IIO >> conversion-delay attribute. >> >> Derive the delay resolution from MCLK, power mode and decimation rate. >> Validate the requested delay and program the corresponding phase >> register when applying the active channel configuration. > ... > >> +static int ad7768_get_convdelay_params(struct ad7768_state *st, unsigned int ch, >> + struct ad7768_convdelay_params *params) >> +{ >> + struct ad7768_freq_config f_cfg; >> + unsigned int dec_rate; >> + unsigned int mclk_div; >> + unsigned int mult; >> + u64 mclk; >> + int ret; >> + >> + ret = ad7768_get_freq_cfg(st, st->ch_freq[ch], &f_cfg); >> + if (ret) >> + return ret; >> + >> + dec_rate = ad7768_dec_rate[f_cfg.dec_rate]; >> + switch (dec_rate) { >> + case 32: >> + params->shift = 3; >> + params->max_raw = 31; >> + mult = 1; >> + break; >> + case 64: >> + params->shift = 2; >> + params->max_raw = 63; >> + mult = 1; >> + break; >> + case 128: >> + params->shift = 1; >> + params->max_raw = 127; >> + mult = 1; >> + break; >> + case 256: >> + params->shift = 0; >> + params->max_raw = 255; >> + mult = 1; >> + break; >> + case 512: >> + params->shift = 0; >> + params->max_raw = 255; >> + mult = 2; >> + break; >> + case 1024: >> + params->shift = 0; >> + params->max_raw = 255; >> + mult = 4; >> + break; >> + default: >> + return -EINVAL; >> + } > So, this is just a bit twiddling of the dec_rate. > > Can be written like > > /* Optional, perhaps shouldn't appear */ > if (!dec_rate) > return -EINVAL; > > /* Same? What does table allow to have? */ > if (!is_power_of_two(dec_rate)) > return -EINVAL; > > mult = ilog2(dec_rate); > if (mult > 10) { > return -EINVAL; > } else if (mult > 8) { > params->shift = 0; > params->max_raw = 255; > mult = BIT(mult - 8); > } else if (mult > 5) { > params->shift = 8 - mult; > params->max_raw = dec_rate - 1; > mult = 1; > } else { > return -EINVAL; > } > > TBH, I don't know which looks easier to read. It all depends on what datasheet > says about these parameters and multiplier and what the table allows to have. > I kept the explicit switch case because it the device supports only the 6 discrete decimation ratios listed in the table 32. The switch directly mirrors the phase resolution, number of steps and register bit mappings from that table, which I find easier to verify against the datasheet. The arithmetic version is more compact, but the proposed conditions would reject the valid x32 case because ilog2(32) is 5. A corrected arithmetic version would be functionally equivalent, but I do not think it improves the readability here. Regards, Jan