From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, andrea.merello@gmail.com,
patrice.chotard@foss.st.com, linux-amlogic@lists.infradead.org
Subject: Re: [PATCH v1 1/2] clocksource/drivers/arm_global_timer: Fix maximum prescaler value
Date: Mon, 19 Feb 2024 00:48:37 +0100 [thread overview]
Message-ID: <5f6229ac-1390-41b5-af91-53799641d3b2@linaro.org> (raw)
In-Reply-To: <CAFBinCC0BbahEMeW9CYC+hKk0CBQ9a+CqNrOv3c92D8hDtQHdQ@mail.gmail.com>
On 19/02/2024 00:18, Martin Blumenstingl wrote:
> Hi Daniel,
>
> On Sun, Feb 18, 2024 at 11:59 PM Daniel Lezcano
> <daniel.lezcano@linaro.org> wrote:
> [...]
>>> #define GT_CONTROL_PRESCALER_SHIFT 8
>>> -#define GT_CONTROL_PRESCALER_MAX 0xF
>>> +#define GT_CONTROL_PRESCALER_MAX 0xFF
>>> #define GT_CONTROL_PRESCALER_MASK (GT_CONTROL_PRESCALER_MAX << \
>>> GT_CONTROL_PRESCALER_SHIFT
>>
>> Good catch!
>>
>> IMO the initial confusion is coming from the shift and the mask size.
>>
>> But should GT_CONTROL_PRESCALER_MAX be 256 ? so (0xFF + 1)
> It depends on what we consider "max" to be:
> - the register value
> - the actual number that's used in the calculation formula
>
> If we ignore the usage of GT_CONTROL_PRESCALER_MAX within
> GT_CONTROL_PRESCALER_MASK then there's only one occurrence left, which
> decrements the calculated value right before comparing it against
> GT_CONTROL_PRESCALER_MAX.
> This means: the remaining driver currently considers
> GT_CONTROL_PRESCALER_MAX to be the maximum value that can be written
> to the register, having converted the value from the calculation
> formula to register value beforehand.
>
>> The following may be less confusing:
>>
>> #define GT_CONTROL_PRESCALER_SHIFT 8
>> #define GT_CONTROL_PRESCALER_MASK GENMASK(15,8)
>> #define GT_CONTROL_PRESCALER_MAX (GT_CONTROL_PRESCALER_MASK >> \
>> GT_CONTROL_PRESCALER_SHIFT) + 1
> If you're interested then I'll work on a follow-up patch to clean up
> the prescaler macros (using FIELD_PREP, FIELD_GET and GENMASK would
> simplify things IMO).
Yes, cleanups are welcome
> I think that this patch is still good as-is since it's small and can
> be backported easily (if someone wants to do that).
Ok, I'm fine with that
--
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next prev parent reply other threads:[~2024-02-18 23:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-18 17:41 [PATCH v1 0/2] clocksource/drivers/arm_global_timer: Two small fixes Martin Blumenstingl
2024-02-18 17:41 ` [PATCH v1 1/2] clocksource/drivers/arm_global_timer: Fix maximum prescaler value Martin Blumenstingl
2024-02-18 22:59 ` Daniel Lezcano
2024-02-18 23:18 ` Martin Blumenstingl
2024-02-18 23:48 ` Daniel Lezcano [this message]
2024-02-18 17:41 ` [PATCH v1 2/2] clocksource/drivers/arm_global_timer: Remove stray tab Martin Blumenstingl
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