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

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Message-ID: <20170215123944.798ae363.john@metanate.com>
Date:   Wed, 15 Feb 2017 12:39:44 +0000
From:   John Keeping <john@...anate.com>
To:     Chris Zhong <zyw@...k-chips.com>
Cc:     Mark Yao <mark.yao@...k-chips.com>,
        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

On Wed, 15 Feb 2017 11:38:45 +0800, Chris Zhong wrote:

> 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.

Nice catch, I'll fix this.

> [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__);  
> 
>