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Wed, 02 Sep 2026 02:02:44 -0700 (PDT) Message-ID: <6dd4c596-aebd-4488-94da-35fb9d85d6ac@suse.com> Date: Wed, 2 Sep 2026 11:02:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] x86/time: CMOS RTC may run in binary mode To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Teddy Astie References: <79d50725-3892-4643-b854-bfec9c0c0d79@suse.com> <5945d8f4-aece-4572-8e89-60408dd7ac32@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-33051d/1788339765-774F44E9-491AD829/0/0 X-purgate-type: clean X-purgate-size: 2433 On 02.09.2026 10:04, Roger Pau Monné wrote: > On Thu, Jul 02, 2026 at 11:29:11AM +0200, Jan Beulich wrote: >> --- a/docs/misc/xen-command-line.pandoc >> +++ b/docs/misc/xen-command-line.pandoc >> @@ -339,6 +339,14 @@ parameter to "stable:socket". >> Specify the event count threshold for raising Corrected Machine Check >> Interrupts. Specifying zero disables CMCI handling. >> >> +### cmos-rtc-bcd (x86) >> +> `= ` >> + >> +> Default: `false` >> + >> +Flag to indicate the CMOS Real Time Clock uses BCD mode irrespective of >> +control register B indicating binary mode. >> + > > Likely too late for it now, but I get the feeling we should have > introduced a cmos option, with rtc-bcd and rtc-probe as boolean sub > options: > > cmos = [ rtc-probe, rtc-bcd ] I was thinking the same - would be nice, but here we are. >> @@ -1353,6 +1356,48 @@ static bool __init cmos_rtc_probe(void) >> return false; >> } >> >> +static inline bool __init attr_const is_bcd(unsigned int x) >> +{ >> + return (x & 0xf) < 10 && (x >> 4) < 10; >> +} >> + >> +static void __init cmos_rtc_probe_bcd(void) >> +{ >> + bool bcd; >> + unsigned long flags; >> + >> + if ( opt_cmos_rtc_bcd ) >> + return; >> + >> + spin_lock_irqsave(&rtc_lock, flags); >> + bcd = !(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY); >> + spin_unlock_irqrestore(&rtc_lock, flags); >> + >> + if ( bcd ) >> + return; >> + >> + for ( unsigned int seclo = 0; ; ) >> + { >> + struct rtc_time rtc; >> + >> + if ( !__get_cmos_time(&rtc) || >> + !is_bcd(rtc.sec) || >> + !is_bcd(rtc.min) || >> + !is_bcd(rtc.hour) || >> + !is_bcd(rtc.day) || >> + !is_bcd(rtc.mon) ) >> + return; >> + >> + if ( seclo > (rtc.sec & 0xf) ) >> + break; >> + >> + seclo = rtc.sec & 0xf; > > Is there a risk of this loop triggering the watchdog, and hence we > should process softirqs in the loop? (or otherwise have some kind of > hard loop stop after certain iterations / time) > > Oh, I now see the mention in the commit message and also note this is > done ahead of SMP and also ahead of the watchdog being enabled, hence > it can't trigger the watchdog. Right. I can't conclude whether you're asking for any change here, as there also was no ack. Jan