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[73.228.159.35]) by smtp.gmail.com with ESMTPSA id e9e14a558f8ab-3df2d32d228sm13202125ab.41.2025.06.25.15.10.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Jun 2025 15:10:56 -0700 (PDT) Message-ID: Date: Wed, 25 Jun 2025 17:10:54 -0500 Precedence: bulk X-Mailing-List: linux-rtc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/7] rtc: spacemit: support the SpacemiT P1 RTC To: Alexandre Belloni Cc: lee@kernel.org, lgirdwood@gmail.com, broonie@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, mat.jonczyk@o2.pl, dlan@gentoo.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, troymitchell988@gmail.com, linux-rtc@vger.kernel.org, devicetree@vger.kernel.org, linux-riscv@lists.infradead.org, spacemit@lists.linux.dev, linux-kernel@vger.kernel.org References: <20250625164119.1068842-1-elder@riscstar.com> <20250625164119.1068842-5-elder@riscstar.com> <202506252201262779aa6c@mail.local> Content-Language: en-US From: Alex Elder In-Reply-To: <202506252201262779aa6c@mail.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/25/25 5:01 PM, Alexandre Belloni wrote: > On 25/06/2025 11:41:15-0500, Alex Elder wrote: >> +/* >> + * The P1 hardware documentation states that the register values are >> + * latched to ensure a consistent time snapshot within the registers, >> + * but these are in fact unstable due to a bug in the hardware design. >> + * So we loop until we get two identical readings. >> + */ >> +static int p1_rtc_read_time(struct device *dev, struct rtc_time *t) >> +{ >> + struct p1_rtc *p1 = dev_get_drvdata(dev); >> + struct regmap *regmap = p1->regmap; >> + u32 count = RTC_READ_TRIES; >> + u8 times[2][6]; >> + size_t size; >> + u32 i = 0; >> + u8 *time; >> + int ret; >> + >> + size = sizeof(times[0]); >> + ret = regmap_bulk_read(regmap, RTC_TIME, times[i], size); >> + if (ret) >> + return ret; >> + >> + do { >> + i = 1 - i; >> + ret = regmap_bulk_read(regmap, RTC_TIME, times[i], size); >> + if (ret) >> + return ret; >> + } while (memcmp(times[i], times[1 - i], size) && --count); > > Simply checking the seconds is enough, unless you expect regmap_bulk_read to ake > more than a minute so you don't need a two dimension array. I hadn't thought it through, but you're right. I'll still do bulk reads but will save only the seconds register and compare it to the previous. > >> + >> + if (!count) >> + return -EIO; >> + >> + time = ×[0][0]; >> + >> + t->tm_sec = time[0] & GENMASK(5, 0); >> + t->tm_min = time[1] & GENMASK(5, 0); >> + t->tm_hour = time[2] & GENMASK(4, 0); >> + t->tm_mday = (time[3] & GENMASK(4, 0)) + 1; >> + t->tm_mon = time[4] & GENMASK(3, 0); >> + t->tm_year = (time[5] & GENMASK(5, 0)) + 100; >> + >> + return 0; >> +} >> + >> +/* >> + * The P1 hardware documentation states that values in the registers are >> + * latched so when written they represent a consistent time snapshot. >> + * Nevertheless, this is not guaranteed by the implementation, so we must >> + * disable the RTC while updating it. >> + */ >> +static int p1_rtc_set_time(struct device *dev, struct rtc_time *t) >> +{ >> + struct p1_rtc *p1 = dev_get_drvdata(dev); >> + struct regmap *regmap = p1->regmap; >> + u8 time[6]; >> + int ret2; >> + int ret; >> + >> + time[0] = t->tm_sec; >> + time[1] = t->tm_min; >> + time[2] = t->tm_hour; >> + time[3] = t->tm_mday - 1; >> + time[4] = t->tm_mon; >> + time[5] = t->tm_year - 100; >> + >> + /* Disable the RTC to update; re-enable again when done */ >> + ret = regmap_update_bits(regmap, RTC_CTRL, RTC_EN, 0); >> + if (ret) >> + return ret; >> + >> + ret = regmap_bulk_write(regmap, RTC_TIME, time, sizeof(time)); >> + > Honnestly, I'd simply go for > > if (ret) > return ret; > > Here, you are trying to set the time, I'm not sure it is worth trying to > reenable the rtc while hoping the previous time has been kept. OK. I normally at least try to return to the original state even when errors occur. I don't know who updates the RTC, but I suppose if any error occurs writing a value they should assume it's "not working". > This also shows that p1_rtc_read_time should check that RTC_EN is set, else it > knows the time has never been set and is invalid. That's a good point. I'll add a check. And with that it should be fine to return without re-enabling. Thanks for your review. I'll wait until tomorrow to send the next version. -Alex >> + ret2 = regmap_update_bits(regmap, RTC_CTRL, RTC_EN, RTC_EN); >> + >> + return ret ? : ret2; /* Return the first error */ > > >> +} >> + >> +static const struct rtc_class_ops p1_rtc_class_ops = { >> + .read_time = p1_rtc_read_time, >> + .set_time = p1_rtc_set_time, >> +}; >> + >> +static int p1_rtc_probe(struct platform_device *pdev) >> +{ >> + struct device *dev = &pdev->dev; >> + struct rtc_device *rtc; >> + struct p1_rtc *p1; >> + >> + p1 = devm_kzalloc(dev, sizeof(*p1), GFP_KERNEL); >> + if (!p1) >> + return -ENOMEM; >> + dev_set_drvdata(dev, p1); >> + >> + p1->regmap = dev_get_regmap(dev->parent, NULL); >> + if (!p1->regmap) >> + return dev_err_probe(dev, -ENODEV, "failed to get regmap\n"); >> + >> + rtc = devm_rtc_allocate_device(dev); >> + if (IS_ERR(rtc)) >> + return dev_err_probe(dev, PTR_ERR(rtc), >> + "error allocating device\n"); >> + p1->rtc = rtc; >> + >> + rtc->ops = &p1_rtc_class_ops; >> + rtc->range_min = RTC_TIMESTAMP_BEGIN_2000; >> + rtc->range_max = RTC_TIMESTAMP_END_2063; >> + >> + clear_bit(RTC_FEATURE_ALARM, rtc->features); >> + clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features); >> + >> + return devm_rtc_register_device(rtc); >> +} >> + >> +static struct platform_driver p1_rtc_driver = { >> + .probe = p1_rtc_probe, >> + .driver = { >> + .name = MOD_NAME, >> + }, >> +}; >> + >> +module_platform_driver(p1_rtc_driver); >> + >> +MODULE_DESCRIPTION("SpacemiT P1 RTC driver"); >> +MODULE_LICENSE("GPL"); >> +MODULE_ALIAS("platform:" MOD_NAME); >> -- >> 2.45.2 >> >