linux-kernel - Re: [PATCH v4] pwm: rzg2l-gpt: Reinitialize the cache value in rzg2l_gpt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ppqewbxcvsqcpp7met6vupmvxaftfjwiefej2c25jw4hoe3c23@lyh7saabrhkd>
Date: Mon, 17 Nov 2025 08:59:41 +0100
From: Uwe Kleine-König <ukleinek@...nel.org>
To: Biju <biju.das.au@...il.com>
Cc: Biju Das <biju.das.jz@...renesas.com>, linux-pwm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>, linux-renesas-soc@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH v4] pwm: rzg2l-gpt: Reinitialize the cache value in
 rzg2l_gpt_disable()

Hello Biju,

On Fri, Nov 14, 2025 at 02:56:01PM +0000, Biju wrote:
> From: Biju Das <biju.das.jz@...renesas.com>
> 
> The rzg2l_gpt_config() test the rzg2l_gpt->period_tick variable. This
> check is not valid, if enabling of a channel happens after disabling all
> the channels as it test against the cached value. Therefore, reinitialize
> the variable rzg2l_gpt->period_tick to 0 in rzg2l_gpt_disable(), when
> all the logical channels of a hardware channel is disabled.
> 
> Cc: stable@...nel.org
> Fixes: 061f087f5d0b ("pwm: Add support for RZ/G2L GPT")
> Signed-off-by: Biju Das <biju.das.jz@...renesas.com>
> ---
> v3->v4:
>  * Split the patch as separate from [1] for easy merging.
>  * Updated commit description
>  * Added comments about the fix in rzg2l_gpt_disable()
> v3:
>  * New patch
> 
> [1] https://lore.kernel.org/all/20250915163637.3572-1-biju.das.jz@bp.renesas.com/#t
> ---
>  drivers/pwm/pwm-rzg2l-gpt.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/pwm-rzg2l-gpt.c b/drivers/pwm/pwm-rzg2l-gpt.c
> index 360c8bf3b190..ab91bfd7da48 100644
> --- a/drivers/pwm/pwm-rzg2l-gpt.c
> +++ b/drivers/pwm/pwm-rzg2l-gpt.c
> @@ -190,8 +190,17 @@ static void rzg2l_gpt_disable(struct rzg2l_gpt_chip *rzg2l_gpt,
>  	/* Stop count, Output low on GTIOCx pin when counting stops */
>  	rzg2l_gpt->channel_enable_count[ch]--;
>  
> -	if (!rzg2l_gpt->channel_enable_count[ch])
> +	if (!rzg2l_gpt->channel_enable_count[ch]) {
>  		rzg2l_gpt_modify(rzg2l_gpt, RZG2L_GTCR(ch), RZG2L_GTCR_CST, 0);
> +		/*
> +		 * The rzg2l_gpt_config() test the rzg2l_gpt->period_tick
> +		 * variable. This check is not valid, if enabling of a channel
> +		 * happens after disabling all the channels as it test against
> +		 * the cached value. Therefore, reinitialize the variable
> +		 * rzg2l_gpt->period_tick to 0.
> +		 */
> +		rzg2l_gpt->period_ticks[ch] = 0;
> +	}

I think this is wrong. rzg2l_gpt_config() has:

        if (rzg2l_gpt->channel_request_count[ch] > 1) {
                if (period_ticks < rzg2l_gpt->period_ticks[ch])
                        return -EBUSY;
                else
                        period_ticks = rzg2l_gpt->period_ticks[ch];
        }

So if both PWMs of channel `ch` are requested but disabled,
rzg2l_gpt->period_ticks[ch] is 0 so you assign

	period_ticks = rzg2l_gpt->period_ticks[ch];

. In that case however you don't want to change period_ticks, right?

Best regards
Uwe

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)