linux-kernel - Re: [PATCH] drm/bridge: ti-sn65dsi86: Implement the pwm

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Message-ID: <20201210130453.regjkemfneqbelsi@pengutronix.de>
Date:   Thu, 10 Dec 2020 14:04:53 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Shawn Guo <shawn.guo@...aro.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Doug Anderson <dianders@...omium.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: ti-sn65dsi86: Implement the pwm_chip

Hi Shawn,

On Thu, Dec 10, 2020 at 09:51:37AM +0800, Shawn Guo wrote:
> On Mon, Dec 07, 2020 at 10:40:22PM -0600, Bjorn Andersson wrote:
> > The SN65DSI86 provides the ability to supply a PWM signal on GPIO 4,
> > with the primary purpose of controlling the backlight of the attached
> > panel. Add an implementation that exposes this using the standard PWM
> > framework, to allow e.g. pwm-backlight to expose this to the user.
> > 
> > Special thanks to Doug Anderson for suggestions related to the involved
> > math.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> >  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 202 ++++++++++++++++++++++++++
> >  1 file changed, 202 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > index f27306c51e4d..43c0acba57ab 100644
> > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > @@ -4,6 +4,7 @@
> >   * datasheet: https://www.ti.com/lit/ds/symlink/sn65dsi86.pdf
> >   */
> >  
> > +#include <linux/atomic.h>
> >  #include <linux/bits.h>
> >  #include <linux/clk.h>
> >  #include <linux/debugfs.h>
> > @@ -14,6 +15,7 @@
> >  #include <linux/module.h>
> >  #include <linux/of_graph.h>
> >  #include <linux/pm_runtime.h>
> > +#include <linux/pwm.h>
> >  #include <linux/regmap.h>
> >  #include <linux/regulator/consumer.h>
> >  
> > @@ -89,6 +91,11 @@
> >  #define SN_ML_TX_MODE_REG			0x96
> >  #define  ML_TX_MAIN_LINK_OFF			0
> >  #define  ML_TX_NORMAL_MODE			BIT(0)
> > +#define SN_PWM_PRE_DIV_REG			0xA0
> > +#define SN_BACKLIGHT_SCALE_REG			0xA1
> > +#define  BACKLIGHT_SCALE_MAX			0xFFFF
> > +#define SN_BACKLIGHT_REG			0xA3
> > +#define SN_PWM_EN_INV_REG			0xA5
> >  #define SN_AUX_CMD_STATUS_REG			0xF4
> >  #define  AUX_IRQ_STATUS_AUX_RPLY_TOUT		BIT(3)
> >  #define  AUX_IRQ_STATUS_AUX_SHORT		BIT(5)
> > @@ -111,6 +118,8 @@
> >  
> >  #define SN_LINK_TRAINING_TRIES		10
> >  
> > +#define SN_PWM_GPIO			3
> 
> So this maps to the GPIO4 described in sn65dsi86 datasheet.  I'm
> wondering if it's more readable to define the following SHIFT constants
> (your code), and use GPIO_MUX_GPIO4_SHIFT >> 2 where you need GPIO
> offset?
> 
> #define  GPIO_MUX_GPIO1_SHIFT	0
> #define  GPIO_MUX_GPIO2_SHIFT	2
> #define  GPIO_MUX_GPIO3_SHIFT	4
> #define  GPIO_MUX_GPIO4_SHIFT	6
> 
> If you agree, you may consider to integrate this patch beforehand:
> 
> https://github.com/shawnguo2/linux/commit/7cde887ffb3b27a36e77a08bee3666d14968b586

My preferred way here would be to add a prefix for the other constants.
It (IMHO) looks nicer and

	GPIO_INPUT_SHIFT

looks like a quite generic name for a hardware specific definition.
(Even if up to now there is no other code location using this name.)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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