Patch "pwm: mtk-disp: Configure double buffering before reading in .get_state()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    pwm: mtk-disp: Configure double buffering before reading in .get_state()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     pwm-mtk-disp-configure-double-buffering-before-readi.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 184a14ed3290e71239ac4046a2455b55c88aef25
Author: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
Date:   Mon Apr 3 15:30:54 2023 +0200

    pwm: mtk-disp: Configure double buffering before reading in .get_state()
    
    [ Upstream commit b16c310115f2084b8826a35b77ef42bab6786d9f ]
    
    The DISP_PWM controller's default behavior is to always use register
    double buffering: all reads/writes are then performed on shadow
    registers instead of working registers and this becomes an issue
    in case our chosen configuration in Linux is different from the
    default (or from the one that was pre-applied by the bootloader).
    
    An example of broken behavior is when the controller is configured
    to use shadow registers, but this driver wants to configure it
    otherwise: what happens is that the .get_state() callback is called
    right after registering the pwmchip and checks whether the PWM is
    enabled by reading the DISP_PWM_EN register;
    At this point, if shadow registers are enabled but their content
    was not committed before booting Linux, we are *not* reading the
    current PWM enablement status, leading to the kernel knowing that
    the hardware is actually enabled when, in reality, it's not.
    
    The aforementioned issue emerged since this driver was fixed with
    commit 0b5ef3429d8f ("pwm: mtk-disp: Fix the parameters calculated
    by the enabled flag of disp_pwm") making it to read the enablement
    status from the right register.
    
    Configure the controller in the .get_state() callback to avoid
    this desync issue and get the backlight properly working again.
    
    Fixes: 3f2b16734914 ("pwm: mtk-disp: Implement atomic API .get_state()")
    Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>
    Reviewed-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
    Tested-by: Nícolas F. R. A. Prado <nfraprado@xxxxxxxxxxxxx>
    Reviewed-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>
    Tested-by: Alexandre Mergnat <amergnat@xxxxxxxxxxxx>
    Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
index 7fea385a387a5..3811578fcff05 100644
--- a/drivers/pwm/pwm-mtk-disp.c
+++ b/drivers/pwm/pwm-mtk-disp.c
@@ -196,6 +196,16 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip,
 		return 0;
 	}
 
+	/*
+	 * Apply DISP_PWM_DEBUG settings to choose whether to enable or disable
+	 * registers double buffer and manual commit to working register before
+	 * performing any read/write operation
+	 */
+	if (mdp->data->bls_debug)
+		mtk_disp_pwm_update_bits(mdp, mdp->data->bls_debug,
+					 mdp->data->bls_debug_mask,
+					 mdp->data->bls_debug_mask);
+
 	rate = clk_get_rate(mdp->clk_main);
 	con0 = readl(mdp->base + mdp->data->con0);
 	con1 = readl(mdp->base + mdp->data->con1);



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