On Sat, 9 Apr 2022 at 00:05, Bjorn Andersson <bjorn.andersson@xxxxxxxxxx> 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@xxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> ---
>
> 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
