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Wed, 13 May 2026 08:08:31 -0700 (PDT) Message-ID: Date: Wed, 13 May 2026 17:08:29 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-4.22 1/5] x86/time: use RTC century byte when available To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Teddy Astie , Oleksii Kurochko References: <2723456f-5d8c-4a2a-9876-e65d35579936@suse.com> <35e23e0f-5439-4516-906c-4310cd05a4a9@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-720697/1778684911-A9772161-CEC50CFB/0/0 X-purgate-type: clean X-purgate-size: 1692 On 13.05.2026 16:51, Roger Pau Monné wrote: > On Wed, May 13, 2026 at 12:36:26PM +0200, Jan Beulich wrote: >> On 13.05.2026 10:49, Roger Pau Monné wrote: >>> On Tue, May 12, 2026 at 04:58:43PM +0200, Jan Beulich wrote: >>>> @@ -1280,6 +1281,8 @@ static bool __get_cmos_time(struct rtc_t >>>> rtc->day = CMOS_READ(RTC_DAY_OF_MONTH); >>>> rtc->mon = CMOS_READ(RTC_MONTH); >>>> rtc->year = CMOS_READ(RTC_YEAR); >>>> + if ( acpi_gbl_FADT.century && acpi_gbl_FADT.century < 0x80 ) >>>> + century = CMOS_READ(acpi_gbl_FADT.century); >>>> >>>> if ( RTC_ALWAYS_BCD || !(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) ) >>>> { >>>> @@ -1293,7 +1296,12 @@ static bool __get_cmos_time(struct rtc_t >>>> >>>> spin_unlock_irqrestore(&rtc_lock, flags); >>>> >>>> - if ( (rtc->year += 1900) < 1970 ) >>>> + if ( century ) >>>> + { >>>> + BCD_TO_BIN(century); >>> >>> Don't you need to move the BCD_TO_BIN() translation with the rest, so >>> it's not done unconditionally? >> >> No, the century field is always BCD. > > Hm, then I guess Linux needs adjusting, as mc146818_set_time() only > converts the century to the BCD format conditionally on the control > register or RTC_ALWAYS_BCD. Hmm, indeed. Btw, while looking there I also noticed this #ifdef CONFIG_ACPI if (p.century > 19) time->tm_year += (p.century - 19) * 100; #endif (relevant to a remark you gave on a later patch in this series). > I've found several sources only that as you mention also claim the > century value is unconditionally in BCD format. > > Acked-by: Roger Pau Monné Thanks. Jan