linux-kernel - RE: [PATCH V1 21/26] DT bindings: spi: add tx/rx clock delay SPI client properties

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Message-ID: <BYAPR12MB33988CD5578E3421E5AB005FC2560@BYAPR12MB3398.namprd12.prod.outlook.com>
Date:   Tue, 2 Apr 2019 20:27:43 +0000
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Rob Herring <robh@...nel.org>
CC:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Timo Alho <talho@...dia.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Krishna Yarlagadda" <kyarlagadda@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH V1 21/26] DT bindings: spi: add tx/rx clock delay SPI
 client properties

> On Tue, Mar 26, 2019 at 10:56:42PM -0700, Sowjanya Komatineni wrote:
> > This patch adds Tegra SPI master tx and rx clock delay properties.
> > 
> > TX/RX clock delays may vary depending on the platform design trace 
> > lengths for each client on the Tegra SPI bus. These properties helps 
> > to tune the clock delays.
> > 
> > Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
> > ---
> >  .../devicetree/bindings/spi/nvidia,tegra114-spi.txt      | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
>
> Just combine this with patch 19.
>
> > diff --git 
> > a/Documentation/devicetree/bindings/spi/nvidia,tegra114-spi.txt 
> > b/Documentation/devicetree/bindings/spi/nvidia,tegra114-spi.txt
> > index 6167c5234b64..2b84b7b726ce 100644
> > --- a/Documentation/devicetree/bindings/spi/nvidia,tegra114-spi.txt
> > +++ b/Documentation/devicetree/bindings/spi/nvidia,tegra114-spi.txt
> > @@ -29,6 +29,12 @@ spi-client device controller properties:
> >  - nvidia,cs-hold-clk-count: CS hold timing parameter.
> >  - nvidia,cs-inactive-cycles: CS inactive delay in terms of clock between
> >    transfers.
> > +- nvidia,tx-clk-tap-delay: Delays the clock going out to the external 
> > +device
> > +  with this tap value. This property is used to tune the outgoing 
> > +data from
> > +  Tegra SPI master with respect to outgoing Tegra SPI master clock.
> > +- nvidia,rx-clk-tap-delay: Delays the clock coming in from the 
> > +external device
> > +  with this tap value. This property is used to adjust the Tegra SPI 
> > +master
> > +  clock with respect to the data from the SPI slave device.
>
> Are there units? What's the range of values.

TX/RX Clock delays are tap counts and there is internal tap-to-tap delay.
Will update to specify tap to delay correlation along with supported tap values range.

As per feedback from mark, will move CS timing to API implementation as they are not
Tegra SPI specific and applicable in general.

>
> >  
> >  Example:
> >  
> > @@ -45,4 +51,14 @@ spi@...0d600 {
> >  	reset-names = "spi";
> >  	dmas = <&apbdma 16>, <&apbdma 16>;
> >  	dma-names = "rx", "tx";
> > +
> > +	<spi-client>@<bus_num> {
> > +		...
> > +		...
> > +		nvidia,cs-setup-clk-count = <10>;
> > +		nvidia,cs-hold-clk-count = <10>;
> > +		nvidia,rx-clk-tap-delay = <0>;
> > +		nvidia,tx-clk-tap-delay = <16>;
> > +		...
> > +	};
> >  };
> > --
> > 2.7.4
> >