linux-kernel - Re: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to power-on sequence

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Date:   Tue, 16 Aug 2022 13:08:18 +0800
From:   Rock Chiu <rock.chiu@...adetech.corp-partner.google.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: ps8640: Add double reset T4 and T5 to
 power-on sequence

Hsin-Yi Wang <hsinyi@...omium.org> 於 2022年8月15日 週一 下午5:39寫道：
>
> The double reset power-on sequence is a workaround for the hardware
> flaw in some chip that SPI Clock output glitch and cause internal MPU
> unable to read firmware correctly. The sequence is suggested in ps8640
> application note.
>
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>

Reviewed-by: Rock Chiu <rock.chiu@...adetech.corp-partner.google.com>
>
> ---
>
>  drivers/gpu/drm/bridge/parade-ps8640.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index 49107a6cdac18..d7483c13c569b 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -375,6 +375,11 @@ static int __maybe_unused ps8640_resume(struct device *dev)
>         gpiod_set_value(ps_bridge->gpio_reset, 1);
>         usleep_range(2000, 2500);
>         gpiod_set_value(ps_bridge->gpio_reset, 0);
> +       /* Double reset for T4 and T5 */
> +       msleep(50);
> +       gpiod_set_value(ps_bridge->gpio_reset, 1);
> +       msleep(50);
> +       gpiod_set_value(ps_bridge->gpio_reset, 0);
>
>         /*
>          * Mystery 200 ms delay for the "MCU to be ready". It's unclear if
> --
> 2.37.1.595.g718a3a8f04-goog
>