Re: [PATCH v6 06/18] video: tegra20: dc: add reset support

["Thierry Reding" <thierry.reding@gmail.com>]

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On Tue Jan 23, 2024 at 6:16 PM CET, Svyatoslav Ryhel wrote:
> Implement reset use to discard any changes which could have been
> applied to DC before and can interfere with current configuration.
>
> Tested-by: Agneli <poczt@protonmail.ch> # Toshiba AC100 T20
> Tested-by: Robert Eckelmann <longnoserob@gmail.com> # ASUS TF101
> Tested-by: Andreas Westman Dorcsak <hedmoo@yahoo.com> # ASUS Grouper E1565
> Tested-by: Ion Agorria <ion@agorria.com> # HTC One X
> Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # Nvidia Tegratab T114
> Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
> ---
>  drivers/video/tegra20/tegra-dc.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/drivers/video/tegra20/tegra-dc.c b/drivers/video/tegra20/tegra-dc.c
> index 56a23b3c97..35abb6fe46 100644
> --- a/drivers/video/tegra20/tegra-dc.c
> +++ b/drivers/video/tegra20/tegra-dc.c
> @@ -10,7 +10,9 @@
>  #include <panel.h>
>  #include <part.h>
>  #include <pwm.h>
> +#include <reset.h>
>  #include <video.h>
> +#include <linux/delay.h>
>  #include <asm/cache.h>
>  #include <asm/global_data.h>
>  #include <asm/system.h>
> @@ -342,6 +344,7 @@ static int tegra_lcd_probe(struct udevice *dev)
>  	struct video_uc_plat *plat = dev_get_uclass_plat(dev);
>  	struct video_priv *uc_priv = dev_get_uclass_priv(dev);
>  	struct tegra_lcd_priv *priv = dev_get_priv(dev);
> +	struct reset_ctl reset_ctl;
>  	int ret;
>  
>  	/* Initialize the Tegra display controller */
> @@ -349,6 +352,20 @@ static int tegra_lcd_probe(struct udevice *dev)
>  	funcmux_select(PERIPH_ID_DISP1, FUNCMUX_DEFAULT);
>  #endif
>  
> +	ret = reset_get_by_name(dev, "dc", &reset_ctl);
> +	if (ret) {
> +		log_err("reset_get_by_name() failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	clock_disable(priv->dc_clk[0]);
> +
> +	/* Reset everything set before */
> +	reset_assert(&reset_ctl);
> +	mdelay(4);
> +	reset_deassert(&reset_ctl);
> +	mdelay(4);

Are you sure this works as intended? It's been a long time since I
worked on this, but I seem to recall that most of these resets are
actually synchronous, so in order for them to do what they're supposed
to the clock needs to be kept running.

The Linux driver certainly does this differently.

Thierry

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