linux-kernel - Re: [PATCH 1/4] rtc: zynqmp: correct frequency value

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Message-ID: <d3087d78-31e6-4a29-8939-d6adae8a4307@vaisala.com>
Date: Wed, 10 Dec 2025 14:29:42 +0200
From: Tomas Melin <tomas.melin@...sala.com>
To: "T, Harini" <Harini.T@....com>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 "Simek, Michal" <michal.simek@....com>
Cc: "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] rtc: zynqmp: correct frequency value

Hi,

On 09/12/2025 18:51, T, Harini wrote:
> [Public]
> 
> Hi,
> 
>> -----Original Message-----
>> From: Tomas Melin <tomas.melin@...sala.com>
>> Sent: Monday, December 1, 2025 6:20 PM
>> To: Alexandre Belloni <alexandre.belloni@...tlin.com>; Simek, Michal
>> <michal.simek@....com>
>> Cc: linux-rtc@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
>> kernel@...r.kernel.org; Tomas Melin <tomas.melin@...sala.com>
>> Subject: [PATCH 1/4] rtc: zynqmp: correct frequency value
>>
>> Caution: This message originated from an External Source. Use proper
>> caution when opening attachments, clicking links, or responding.
>>
>>
>> Fix calibration value in case a clock reference is provided.
>> The actual calibration value written into register is
>> frequency - 1.
>>
>> Signed-off-by: Tomas Melin <tomas.melin@...sala.com>
>> ---
>>  drivers/rtc/rtc-zynqmp.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/rtc/rtc-zynqmp.c b/drivers/rtc/rtc-zynqmp.c
>> index
>> 3baa2b481d9f2008750046005283b98a0d546c5c..856bc1678e7d31144f320ae
>> 9f75fc58c742a2a64 100644
>> --- a/drivers/rtc/rtc-zynqmp.c
>> +++ b/drivers/rtc/rtc-zynqmp.c
>> @@ -345,7 +345,10 @@ static int xlnx_rtc_probe(struct platform_device
>> *pdev)
>>                                            &xrtcdev->freq);
>>                 if (ret)
>>                         xrtcdev->freq = RTC_CALIB_DEF;
>> +       } else {
>> +               xrtcdev->freq--;
> If freq > 65536, the 16-bit register silently truncates.
> Please add some checks for above mentioned scenario.
That is indeed a scenario that is not accounted for in the current
driver. I can add a separate patch for that as part of this series.

Thanks,
Tomas


>>         }
>> +
>>         ret = readl(xrtcdev->reg_base + RTC_CALIB_RD);
>>         if (!ret)
>>                 writel(xrtcdev->freq, (xrtcdev->reg_base + RTC_CALIB_WR));
>>
>> --
>> 2.47.3
>>
> Thanks,
> Harini T