linux-kernel - Re: [PATCH] arm_mpam: Fix T241-MPAM-4 workaround

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Message-ID: <20240821124247.000067fc@Huawei.com>
Date: Wed, 21 Aug 2024 12:42:47 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Shanker Donthineni <sdonthineni@...dia.com>
CC: James Morse <james.morse@....com>, Catalin Marinas
	<catalin.marinas@....com>, Rohit Mathew <rohit.mathew@....com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Vikram Sethi <vsethi@...dia.com>
Subject: Re: [PATCH] arm_mpam: Fix T241-MPAM-4 workaround

On Mon, 19 Aug 2024 17:08:18 -0500
Shanker Donthineni <sdonthineni@...dia.com> wrote:

> The workaround for T241-MPAM-4 was applied incorrectly, leading to
> MBW_MIN being programmed with a zero value when the user specifies
> MBW_MAX is less than 5%.
> 
> This patch ensures that MBW_MIN is programmed with a non-zero value,
> set to 1 to fix the T241-MPAM-4 as expected.
> 
> Fixes: 13ff1b527e40 ("arm_mpam: Add workaround for T241-MPAM-4")
> Signed-off-by: Shanker Donthineni <sdonthineni@...dia.com>
Hi Shanker,

I can guess which branch this fix is for, but good to mention it
in the patch given it's not mainline.

Jonathan

> ---
>  drivers/platform/arm64/mpam/mpam_devices.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/arm64/mpam/mpam_devices.c b/drivers/platform/arm64/mpam/mpam_devices.c
> index a802ca1c9f05..e49a27c02c66 100644
> --- a/drivers/platform/arm64/mpam/mpam_devices.c
> +++ b/drivers/platform/arm64/mpam/mpam_devices.c
> @@ -2990,7 +2990,7 @@ static void mpam_extend_config(struct mpam_class *class, struct mpam_config *cfg
>  	}
>  
>  	if (mpam_has_quirk(T241_FORCE_MBW_MIN_TO_ONE, class) &&
> -	    cfg->mbw_min == 0) {
> +	    cfg->mbw_min <= min_hw_granule) {
>  		cfg->mbw_min = min_hw_granule + 1;
>  		mpam_set_feature(mpam_feat_mbw_min, cfg);
>  	}