linux-kernel - Re: [PATCH v1] pwm: microchip-core: fix incorrect comparison with max period

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Message-ID: <r3dybh3ef4lbneruiae4s5co6mkgsowwucba6niqv23tfycyza@qnklz4w5rnnr>
Date: Thu, 23 Jan 2025 16:15:57 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Conor Dooley <conor@...nel.org>
Cc: linux-pwm@...r.kernel.org, Conor Dooley <conor.dooley@...rochip.com>, 
	stable@...r.kernel.org, Daire McNamara <daire.mcnamara@...rochip.com>, 
	Thierry Reding <thierry.reding@...il.com>, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] pwm: microchip-core: fix incorrect comparison with
 max period

Hello Conor,

On Wed, Jan 22, 2025 at 02:42:56PM +0000, Conor Dooley wrote:
> From: Conor Dooley <conor.dooley@...rochip.com>
> 
> In mchp_core_pwm_apply_locked(), if hw_period_steps is equal to its max,
> an error is reported and .apply fails. The max value is actually a
> permitted value however, and so this check can fail where multiple
> channels are enabled.
> 
> For example, the first channel to be configured requests a period that
> sets hw_period_steps to the maximum value, and when a second channel
> is enabled the driver reads hw_period_steps back from the hardware and
> finds it to be the maximum possible value, triggering the warning on a
> permitted value. The value to be avoided is 255 (PERIOD_STEPS_MAX + 1),
> as that will produce undesired behaviour, so test for greater than,
> rather than equal to.
> 
> Fixes: 2bf7ecf7b4ff ("pwm: add microchip soft ip corePWM driver")
> CC: stable@...r.kernel.org
> Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>

Applied to

	https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux.git pwm/fixes

which I intend to send to Linus next week.

Best regards
Uwe

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