linux-kernel - Re: [PATCH 2/3] drm: bridge: it66121: Fix the register page length

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Date:   Fri, 18 Mar 2022 09:34:19 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Nicolas Belin <nbelin@...libre.com>, andrzej.hajda@...el.com,
        robert.foss@...aro.org
Cc:     devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com
Subject: Re: [PATCH 2/3] drm: bridge: it66121: Fix the register page length

On 16/03/2022 14:57, Nicolas Belin wrote:
> Set the register page length or window length to
> 0x100 according to the documentation.
> 
> Fixes: 988156dc2fc9 ("drm: bridge: add it66121 driver")
> Signed-off-by: Nicolas Belin <nbelin@...libre.com>
> ---
>   drivers/gpu/drm/bridge/ite-it66121.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> index 06b59b422c69..64912b770086 100644
> --- a/drivers/gpu/drm/bridge/ite-it66121.c
> +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> @@ -227,7 +227,7 @@ static const struct regmap_range_cfg it66121_regmap_banks[] = {
>   		.selector_mask = 0x1,
>   		.selector_shift = 0,
>   		.window_start = 0x00,
> -		.window_len = 0x130,
> +		.window_len = 0x100,
>   	},
>   };
>   

The documentation we have access to at [1] is confusing:
Reg00 ~ Reg2F are accessible in any register bank.
Reg30~ RegFF are accessible in register bank0
Reg130~ Reg1BF are accessible in register bank1. These are HDMI packet registers.

But indeed it means:
- Reg00 ~ Reg2F: are always accessible, whether bank0 or bank1 is set
- Reg30~ RegFF: only when bank0 is set
- Reg130~ Reg1BF: only when bank0 is set at Reg30~ RegF range

So 0x100 is the right window_len here.

Acked-by: Neil Armstrong <narmstrong@...libre.com>

[1] https://rockchip.fr/radxa/IT66121_Register_List_Release_V1.0.pdf