Date: Tue, 19 Sep 2017 13:27:40 -0700
From: Sean Paul <seanpaul@chromium.org>
To: Brian Norris <briannorris@chromium.org>
Cc: Sean Paul <seanpaul@chromium.org>,
        Nickey Yang <nickey.yang@rock-chips.com>, mark.yao@rock-chips.com,
        robh+dt@kernel.org, heiko@sntech.de, mark.rutland@arm.com,
        airlied@linux.ie, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org,
        hl@rock-chips.com, zyw@rock-chips.com, bivvy.bi@rock-chips.com,
        xbl@rock-chips.com
Subject: Re: [PATCH 1/7] drm/rockchip/dsi: correct Feedback divider setting
Message-ID: <20170919202740.2ku56pefrj3wyskw@art_vandelay>
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 <20170919180025.apb4aq7ca3filh6c@art_vandelay>
 <20170919181751.GA38656@google.com>
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On Tue, Sep 19, 2017 at 11:19:01AM -0700, Brian Norris wrote:
> Hi Sean,
> 
> On Tue, Sep 19, 2017 at 11:00:25AM -0700, Sean Paul wrote:
> > On Mon, Sep 18, 2017 at 05:05:33PM +0800, Nickey Yang wrote:
> > > This patch correct Feedback divider setting:
> > > 1、Set Feedback divider [8:5] when HIGH_PROGRAM_EN
> > > 2、Due to the use of a "by 2 pre-scaler," the range of the
> > > feedback multiplication Feedback divider is limited to even
> > > division numbers, and Feedback divider must be greater than
> > > 12, less than 1000.
> > > 3、Make the previously configured Feedback divider(LSB)
> > > factors effective
> > > 
> > > Signed-off-by: Nickey Yang <nickey.yang@rock-chips.com>
> > > ---
> > >  drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 83 ++++++++++++++++++++++------------
> > >  1 file changed, 54 insertions(+), 29 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> > > index 9a20b9d..52698b7 100644
> > > --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> > > +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> > > @@ -228,7 +228,7 @@
> > >  #define LOW_PROGRAM_EN		0
> > >  #define HIGH_PROGRAM_EN		BIT(7)
> > >  #define LOOP_DIV_LOW_SEL(val)	(((val) - 1) & 0x1f)
> > > -#define LOOP_DIV_HIGH_SEL(val)	((((val) - 1) >> 5) & 0x1f)
> > > +#define LOOP_DIV_HIGH_SEL(val)	((((val) - 1) >> 5) & 0xf)
> > >  #define PLL_LOOP_DIV_EN		BIT(5)
> > >  #define PLL_INPUT_DIV_EN	BIT(4)
> > >  
> > > @@ -461,6 +461,7 @@ static int dw_mipi_dsi_phy_init(struct dw_mipi_dsi *dsi)
> > >  	dw_mipi_dsi_phy_write(dsi, 0x17, INPUT_DIVIDER(dsi->input_div));
> > >  	dw_mipi_dsi_phy_write(dsi, 0x18, LOOP_DIV_LOW_SEL(dsi->feedback_div) |
> > >  					 LOW_PROGRAM_EN);
> > > +	dw_mipi_dsi_phy_write(dsi, 0x19, PLL_LOOP_DIV_EN | PLL_INPUT_DIV_EN);
> > 
> > You do the same write 2 lines down. Are both needed? It would be nice if the
> > register names were also defined, so this is easier to read.
> 
> If I'm reading correctly, I think this is what Nickey meant by:
> 
> "3、Make the previously configured Feedback divider(LSB)
> factors effective"
> 
> . My reading of the databook is that this step finalizes the previous
> two writes (to test code 0x17 and 0x18).
> 
> Given this was buggy (?) previously, it does seem like having some extra
> language to document this could help. Register names (or "test codes",
> per the docs?) could help, but additionally, maybe a few more comments.
> 

Ah, yeah, thanks for the explanation. It's not clear that this latches the 
values above. I think register names and comments would be immensely helpful.

Sean

> > >  	dw_mipi_dsi_phy_write(dsi, 0x18, LOOP_DIV_HIGH_SEL(dsi->feedback_div) |
> > >  					 HIGH_PROGRAM_EN);
> > >  	dw_mipi_dsi_phy_write(dsi, 0x19, PLL_LOOP_DIV_EN | PLL_INPUT_DIV_EN);
> 
> [...]
> 
> Brian

-- 
Sean Paul, Software Engineer, Google / Chromium OS