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

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Date:   Sat, 17 Aug 2019 21:47:54 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        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

On Wed, Aug 07, 2019 at 08:49:52AM +0000, David Laight wrote:
>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.

This looks like an upstream problem as well, no?

--
Thanks,
Sasha