linux-kernel - RE: [PATCH AUTOSEL 5.2 51/59] drm/exynos: fix missing decrement of retry counter

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Message-ID: <2ecde45912fc44b88df2ff5129b8ab67@AcuMS.aculab.com>
Date:   Wed, 7 Aug 2019 08:49:52 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Sasha Levin' <sashal@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Colin Ian King <colin.king@...onical.com>,
        Inki Dae <inki.dae@...sung.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: RE: [PATCH AUTOSEL 5.2 51/59] drm/exynos: fix missing decrement of
 retry counter

From: Sasha Levin
> Sent: 06 August 2019 22:33
> 
> From: Colin Ian King <colin.king@...onical.com>
> 
> [ Upstream commit 1bbbab097a05276e312dd2462791d32b21ceb1ee ]
> 
> Currently the retry counter is not being decremented, leading to a
> potential infinite spin if the scalar_reads don't change state.
> 
> Addresses-Coverity: ("Infinite loop")
> Fixes: 280e54c9f614 ("drm/exynos: scaler: Reset hardware before starting the operation")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> Signed-off-by: Inki Dae <inki.dae@...sung.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_scaler.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_scaler.c b/drivers/gpu/drm/exynos/exynos_drm_scaler.c
> index ec9c1b7d31033..8989f8af716b7 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_scaler.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_scaler.c
> @@ -94,12 +94,12 @@ static inline int scaler_reset(struct scaler_context *scaler)
>  	scaler_write(SCALER_CFG_SOFT_RESET, SCALER_CFG);
>  	do {
>  		cpu_relax();
> -	} while (retry > 1 &&
> +	} while (--retry > 1 &&
>  		 scaler_read(SCALER_CFG) & SCALER_CFG_SOFT_RESET);
>  	do {
>  		cpu_relax();
>  		scaler_write(1, SCALER_INT_EN);
> -	} while (retry > 0 && scaler_read(SCALER_INT_EN) != 1);
> +	} while (--retry > 0 && scaler_read(SCALER_INT_EN) != 1);
> 
>  	return retry ? 0 : -EIO;

If the first loop hits the retry limit the second loop won't be right
and the final return value will be 0.

	David

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