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

From: John Keeping <john@metanate.com>
To: Chris Zhong <zyw@rock-chips.com>
Cc: Mark Yao <mark.yao@rock-chips.com>,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 23/24] drm/rockchip: dw-mipi-dsi: add reset control
Date: Thu, 16 Feb 2017 14:11:04 +0000	[thread overview]
Message-ID: <20170216141104.5ecca1df.john@metanate.com> (raw)
In-Reply-To: <58A50A91.6010202@rock-chips.com>

On Thu, 16 Feb 2017 10:12:33 +0800, Chris Zhong wrote:

> On 02/15/2017 08:39 PM, John Keeping wrote:
> > 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@metanate.com>
> >>> Reviewed-by: Chris Zhong <zyw@rock-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@free.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@free.fr>
> >>       Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
> >>
> >>  
> >>> +			apb_rst = NULL;
> >>> +		} else {
> >>> +			dev_err(dev, "Unable to get reset control: %d\n", ret);  
> Also, we can not get error number from "ret" here.

Good point, I'll fix this.

John