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SubjectRe: [PATCH v4 2/2] drm/msm/dpu: Issue MDSS reset during initialization
From
On 21/04/2022 07:15, Bjorn Andersson 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@linaro.org>

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

> ---
>
> Changes since v3:
> - Rebased upon the mdss dpu/mdp restructuring (https://patchwork.freedesktop.org/series/98525/)
>
> drivers/gpu/drm/msm/msm_mdss.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/msm_mdss.c b/drivers/gpu/drm/msm/msm_mdss.c
> index f6f0d0fa5ab2..20f154dda9cf 100644
> --- a/drivers/gpu/drm/msm/msm_mdss.c
> +++ b/drivers/gpu/drm/msm/msm_mdss.c
> @@ -4,11 +4,13 @@
> */
>
> #include <linux/clk.h>
> +#include <linux/delay.h>
> #include <linux/irq.h>
> #include <linux/irqchip.h>
> #include <linux/irqdesc.h>
> #include <linux/irqchip/chained_irq.h>
> #include <linux/pm_runtime.h>
> +#include <linux/reset.h>
>
> #include "msm_drv.h"
> #include "msm_kms.h"
> @@ -193,6 +195,32 @@ static void msm_mdss_destroy(struct msm_mdss *msm_mdss)
> irq_set_chained_handler_and_data(irq, NULL, NULL);
> }
>
> +static int msm_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)) {
> + return dev_err_probe(dev, PTR_ERR(reset),
> + "failed to acquire mdss reset\n");
> + }
> +
> + 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;
> +}
> +
> /*
> * MDP5 MDSS uses at most three specified clocks.
> */
> @@ -229,6 +257,10 @@ static struct msm_mdss *msm_mdss_init(struct platform_device *pdev, bool is_mdp5
> int ret;
> int irq;
>
> + ret = msm_mdss_reset(&pdev->dev);
> + if (ret)
> + return ERR_PTR(ret);
> +
> msm_mdss = devm_kzalloc(&pdev->dev, sizeof(*msm_mdss), GFP_KERNEL);
> if (!msm_mdss)
> return ERR_PTR(-ENOMEM);


--
With best wishes
Dmitry

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