linux-kernel - Re: drm/exynos: scaler: Reset hardware before starting the operation (bug report)

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Message-ID: <c67b4671-aabc-df13-e9c7-ccbc25337b7c@canonical.com>
Date:   Fri, 5 Jul 2019 17:09:06 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Inki Dae <inki.dae@...sung.com>,
        linux-samsung-soc@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: drm/exynos: scaler: Reset hardware before starting the operation
 (bug report)

Hi,

Static analysis on today's linux-next has found a potential error in the
following commit:

commit 280e54c9f614c88292685383cf2d65057586e9fb
Author: Andrzej Pietrasiewicz <andrzej.p@...sung.com>
Date:   Thu Jun 7 13:06:08 2018 +0200

    drm/exynos: scaler: Reset hardware before starting the operation

In the following code the retry counter does not appear to be
decremented, so potentially the loop could get stuck forever if the H/W
does not change state:

static inline int scaler_reset(struct scaler_context *scaler)
{
        int retry = SCALER_RESET_WAIT_RETRIES;

        scaler_write(SCALER_CFG_SOFT_RESET, SCALER_CFG);
        do {
                cpu_relax();
        } 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);

        return retry ? 0 : -EIO;
}

Maybe I'm missing something here subtle.

Colin