linux-kernel - Re: [PATCH RFC v8 11/21] Documentation: dt-bindings: Add bindings for Synopsys DW MIPI DSI DRM bridge driver

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Message-ID: <20150211140931.GA6666@victor>
Date:	Wed, 11 Feb 2015 22:09:32 +0800
From:	Liu Ying <Ying.Liu@...escale.com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
CC:	<stefan.wahren@...e.com>, <devicetree@...r.kernel.org>,
	<linux@....linux.org.uk>, <andyshrk@...il.com>,
	<linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<a.hajda@...sung.com>, <kernel@...gutronix.de>,
	<mturquette@...aro.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC v8 11/21] Documentation: dt-bindings: Add bindings
 for Synopsys DW MIPI DSI DRM bridge driver

Hi Philipp,

On Wed, Feb 11, 2015 at 02:00:48PM +0100, Philipp Zabel wrote:
> Hi Liu,
> 
> Am Mittwoch, den 11.02.2015, 15:21 +0800 schrieb Liu Ying:
> [...]
> > Our internal MIPI DSI SoC owner gave me some feedbacks on the clock sources.
> > According to him, the Synopsys DesignWare MIPI DSI host controller needs four
> > clock sources from an application platform - pclk, refclk, cfg_clk and dpipclk.
> > These clocks are mentioned in the "DesignWare Cores MIPI DSI Host Controller
> > Databook, 1.01a1.30a.pdf" documentation.
> > 
> > Quote some words from the documentation:
> > pclk    - APB clock signal.
> > refclk  - D-PHY reference clock used for Master-side serial clock generation in
> >           clock multiplying unit(PLL).
> > cfg_clk - D-PHY Configuration clock used for the initialization of the PHY. It
> >           is also used for exiting ULPS state.
> > dpipclk - Input Pixel clock signal.
> > 
> > The below table reflects how does i.MX6Q/DL provide the pclk, refclk and cfg_clk
> > for the DesignWare MIPI DSI host controller, according to the SoC owner.
> >  ----------------------------------------------------------------------------
> > | Synopsys      |                     i.MX6Q/DL MIPI DSI                     |
> > | DesignWare    |------------------------------------------------------------|
> > | documentation |    clock   |     clock root     |       CCM_CCGR bits      |
> > |---------------|------------|--------------------|--------------------------|
> > |     pclk      |   ips_clk  |    ipg_clk_root    | mipi_core_cfg_clk_enable |
> > |---------------|------------|--------------------|--------------------------|
> > |    refclk     | pll_refclk | video_27m_clk_root | mipi_core_cfg_clk_enable |
> > |---------------|------------|--------------------|--------------------------|
> > |    cfg_clk    |   cfg_clk  | video_27m_clk_root | mipi_core_cfg_clk_enable |
> >  ----------------------------------------------------------------------------
> > 
> > I think we should add a new clock "IMX6QDL_CLK_MIPI_IPG" as a shared clock gate
> > clock.
> 
> That would be necessary if the pclk clock rate mattered or would be set
> anywhere.

I don't think the pclk clock rate matters a lot.  It should be sufficient
for the driver only to enable/disable the pclk for registers access, just
like the way the pwm-imx driver uses the ipg clock.

> 
> > And, the clock-names property should exactly contain "pclk", "refclk"
> > and "cfg_clk", right?
> 
> My personal preference would be to drop the superfluous "clk" prefix if
> the resulting clock name is still clearly relatable to the official
> name. Existing clock naming for the pclk is a bit mixed -
> The "snps,dw-apb-timer" binding uses "pclk", which seems to be quite
> common in other places, too. The "snps,dw-apb-uart" bindings use
> "apb_pclk". "snps,dw-hdmi-tx" uses "iahb" and "isfr" without the clk
> suffix.
> How about "pclk", "ref" and "cfg"?

Looks good and clear enough.  I'd like to use them.  Thanks.

BTW, regarding the compatible string topic, shall I keep my implementation
unchanged and don't append the additional "snps,dw-mipi-dsi" as I shared
my concerns about it before?

Regards,
Liu Ying

> 
> regards
> Philipp
> 
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