linux-kernel - Re: [PATCH v3 23/24] drm/rockchip: dw-mipi-dsi: add reset control

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Message-ID: <58A3CD45.9090309@rock-chips.com>
Date:   Wed, 15 Feb 2017 11:38:45 +0800
From:   Chris Zhong <zyw@...k-chips.com>
To:     John Keeping <john@...anate.com>,
        Mark Yao <mark.yao@...k-chips.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 23/24] drm/rockchip: dw-mipi-dsi: add reset control

Hi John

On 01/29/2017 09:24 PM, John Keeping wrote:
> In order to fully reset the state of the MIPI controller we must assert
> this reset.
>
> This is slightly more complicated than it could be in order to maintain
> compatibility with device trees that do not specify the reset property.
>
> Signed-off-by: John Keeping <john@...anate.com>
> Reviewed-by: Chris Zhong <zyw@...k-chips.com>
> ---
> v3:
> - Add Chris' Reviewed-by
> Unchanged in v2
>
>   drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 30 ++++++++++++++++++++++++++++++
>   1 file changed, 30 insertions(+)
>
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index 58cb8ace2fe8..cf3ca6b0cbdb 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -13,6 +13,7 @@
>   #include <linux/module.h>
>   #include <linux/of_device.h>
>   #include <linux/regmap.h>
> +#include <linux/reset.h>
>   #include <linux/mfd/syscon.h>
>   #include <drm/drm_atomic_helper.h>
>   #include <drm/drm_crtc.h>
> @@ -1124,6 +1125,7 @@ static int dw_mipi_dsi_bind(struct device *dev, struct device *master,
>   			of_match_device(dw_mipi_dsi_dt_ids, dev);
>   	const struct dw_mipi_dsi_plat_data *pdata = of_id->data;
>   	struct platform_device *pdev = to_platform_device(dev);
> +	struct reset_control *apb_rst;
>   	struct drm_device *drm = data;
>   	struct dw_mipi_dsi *dsi;
>   	struct resource *res;
> @@ -1162,6 +1164,34 @@ static int dw_mipi_dsi_bind(struct device *dev, struct device *master,
>   		return ret;
>   	}
>   
> +	/*
> +	 * Note that the reset was not defined in the initial device tree, so
> +	 * we have to be prepared for it not being found.
> +	 */
> +	apb_rst = devm_reset_control_get(dev, "apb");
> +	if (IS_ERR(apb_rst)) {
> +		if (PTR_ERR(apb_rst) == -ENODEV) {
According to [0], I think it should be -ENOENT here.

[0]
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=3d81216fde465e76c5eae98f61d3666163634395

commit 3d81216fde465e76c5eae98f61d3666163634395
Author: Alban Bedel <albeu@...e.fr>
Date:   Tue Sep 1 17:28:31 2015 +0200

     reset: Fix of_reset_control_get() for consistent return values

     When of_reset_control_get() is called without connection ID it returns
     -ENOENT when the 'resets' property doesn't exists or is an empty entry.
     However when a connection ID is given it returns -EINVAL when the 
'resets'
     property doesn't exists or the requested name can't be found. This is
     because the error code returned by of_property_match_string() is just
     passed down as an index to of_parse_phandle_with_args(), which then
     returns -EINVAL.

     To get a consistent return value with both code paths we must return
     -ENOENT when of_property_match_string() fails.

     Signed-off-by: Alban Bedel <albeu@...e.fr>
     Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>


> +			apb_rst = NULL;
> +		} else {
> +			dev_err(dev, "Unable to get reset control: %d\n", ret);
> +			return PTR_ERR(apb_rst);
> +		}
> +	}
> +
> +	if (apb_rst) {
> +		ret = clk_prepare_enable(dsi->pclk);
> +		if (ret) {
> +			dev_err(dev, "%s: Failed to enable pclk\n", __func__);
> +			return ret;
> +		}
> +
> +		reset_control_assert(apb_rst);
> +		usleep_range(10, 20);
> +		reset_control_deassert(apb_rst);
> +
> +		clk_disable_unprepare(dsi->pclk);
> +	}
> +
>   	ret = clk_prepare_enable(dsi->pllref_clk);
>   	if (ret) {
>   		dev_err(dev, "%s: Failed to enable pllref_clk\n", __func__);