linux-kernel - Re: [PATCH v3 2/2] drm/msm/dpu: Issue MDSS reset during initialization

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Message-ID: <CAA8EJprnEBcno+TtDGTboWw=dzDqb_Qiy8PEffrN3GcOWv9-wA@mail.gmail.com>
Date:   Sat, 9 Apr 2022 03:18:13 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] drm/msm/dpu: Issue MDSS reset during initialization

On Sat, 9 Apr 2022 at 00:05, Bjorn Andersson <bjorn.andersson@...aro.org> wrote:
>
> It's typical for the bootloader to bring up the display for showing a
> boot splash or efi framebuffer. But in some cases the kernel driver ends
> up only partially configuring (in particular) the DPU, which might
> result in e.g. that two different data paths attempts to push data to
> the interface - with resulting graphical artifacts.
>
> Naturally the end goal would be to inherit the bootloader's
> configuration and provide the user with a glitch free handover from the
> boot configuration to a running DPU.
>
> But as implementing seamless transition from the bootloader
> configuration to the running OS will be a considerable effort, start by
> simply resetting the entire MDSS to its power-on state, to avoid the
> partial configuration.
>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>


> ---
>
> Changes since v2:
> - Move the reset before the probing of the children, to avoid issues if child
>   drivers touched hardware at probe time.
> - Extend reset assert time as the previous 1us showed reliability issues on
>   Lenovo Flex 5G.
>
>  drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c | 32 ++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
> index b10ca505f9ac..6f921910d0e0 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
> @@ -3,10 +3,12 @@
>   * Copyright (c) 2018, The Linux Foundation
>   */
>
> +#include <linux/delay.h>
>  #include <linux/irq.h>
>  #include <linux/irqchip.h>
>  #include <linux/irqdesc.h>
>  #include <linux/irqchip/chained_irq.h>
> +#include <linux/reset.h>
>  #include "dpu_kms.h"
>
>  #define to_dpu_mdss(x) container_of(x, struct dpu_mdss, base)
> @@ -197,6 +199,32 @@ static void dpu_mdss_destroy(struct msm_mdss *mdss)
>         dpu_mdss->mmio = NULL;
>  }
>
> +static int dpu_mdss_reset(struct device *dev)
> +{
> +       struct reset_control *reset;
> +
> +       reset = reset_control_get_optional_exclusive(dev, NULL);
> +       if (!reset) {
> +               /* Optional reset not specified */
> +               return 0;
> +       } else if (IS_ERR(reset)) {
> +               DPU_ERROR("failed to acquire mdss reset, ret=%ld", PTR_ERR(reset));
> +               return PTR_ERR(reset);
> +       }
> +
> +       reset_control_assert(reset);
> +       /*
> +        * Tests indicate that reset has to be held for some period of time,
> +        * make it one frame in a typical system
> +        */
> +       msleep(20);
> +       reset_control_deassert(reset);
> +
> +       reset_control_put(reset);
> +
> +       return 0;
> +}
> +
>  static const struct msm_mdss_funcs mdss_funcs = {
>         .enable = dpu_mdss_enable,
>         .disable = dpu_mdss_disable,
> @@ -210,6 +238,10 @@ int dpu_mdss_init(struct platform_device *pdev)
>         int ret;
>         int irq;
>
> +       ret = dpu_mdss_reset(&pdev->dev);
> +       if (ret)
> +               return ret;
> +
>         dpu_mdss = devm_kzalloc(&pdev->dev, sizeof(*dpu_mdss), GFP_KERNEL);
>         if (!dpu_mdss)
>                 return -ENOMEM;
> --
> 2.35.1
>


-- 
With best wishes
Dmitry