linux-kernel - Re: [PATCH v12 1/4] dt-bindings: spi: Add schema for Cadence QSPI Controller driver

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Message-ID: <c2ad909e-9042-6ba0-7213-83346c6b9908@ti.com>
Date:   Fri, 20 Mar 2020 11:35:57 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     "Ramuthevar,Vadivel MuruganX" 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <broonie@...nel.org>, <robh+dt@...nel.org>
CC:     <devicetree@...r.kernel.org>, <boris.brezillon@...e-electrons.com>,
        <simon.k.r.goldschmidt@...il.com>, <dinguyen@...nel.org>,
        <tien.fong.chee@...el.com>, <marex@...x.de>,
        <linux-mtd@...ts.infradead.org>, <dwmw2@...radead.org>,
        <richard@....at>, <computersforpeace@...il.com>,
        <cyrille.pitchen@...el.com>, <david.oberhollenzer@...ma-star.at>,
        <miquel.raynal@...tlin.com>, <tudor.ambarus@...il.com>,
        <cheol.yong.kim@...el.com>, <qi-ming.wu@...el.com>
Subject: Re: [PATCH v12 1/4] dt-bindings: spi: Add schema for Cadence QSPI
 Controller driver



On 10/03/20 7:22 am, Ramuthevar,Vadivel MuruganX wrote:
> From: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@...ux.intel.com>
> 
> Add dt-bindings documentation for Cadence-QSPI controller to support
> spi based flash memories.
> 
> Signed-off-by: Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@...ux.intel.com>
> ---
>  .../devicetree/bindings/mtd/cadence-quadspi.txt    |  67 -----------
>  .../devicetree/bindings/spi/cdns,qspi-nor.yaml     | 127 +++++++++++++++++++++
>  2 files changed, 127 insertions(+), 67 deletions(-)
>  delete mode 100644 Documentation/devicetree/bindings/mtd/cadence-quadspi.txt
>  create mode 100644 Documentation/devicetree/bindings/spi/cdns,qspi-nor.yaml
> 
[...]

> +
> +# subnode's properties
> +patternProperties:
> +  "^.*@[0-9a-fA-F]+$":
> +    type: object
> +    description:
> +      flash device uses the subnodes below defined properties.
> +
> +  cdns,read-delay:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Delay in 4 microseconds, read capture logic, in clock cycles.


Not its not... See the old binding description please:

-- cdns,read-delay : Delay for read capture logic, in clock cycles

There is no mention of 4us. Range is 0x0 - 0xF

> +
> +  cdns,tshsl-ns:
> +    description: |
> +      Delay in 50 nanoseconds, for the length that the master mode chip select
> +      outputs are de-asserted between transactions.

Again see the description in old binding file:

 cdns,tshsl-ns : Delay in nanoseconds for the length that the master
                  mode chip select outputs are de-asserted between
	  	transactions.

Need not be 50ns or its multiple

> +
> +  cdns,tsd2d-ns:
> +    description: |
> +      Delay in 50 nanoseconds, between one chip select being de-activated
> +      and the activation of another.
> +

same here

> +  cdns,tchsh-ns:
> +    description: |
> +      Delay in 4 nanoseconds, between last bit of current transaction and
> +      deasserting the device chip select (qspi_n_ss_out).
> +

Same here... Need not be 4ns...

> +  cdns,tslch-ns:
> +    description: |
> +      Delay in 4 nanoseconds, between setting qspi_n_ss_out low and
> +      first bit transfer.


Same here...

Above four values ( cdns,*-ns) come directly from the flash datasheets.

These values are converted appropriate number of cycles depending upon
the QSPI ref_clk frequency. So, there is no easy way to express the
constraint (or range) in DT schema. I would recommend to just stick with
the description that is there in the old binding file without any
modifications.

Regards
Vignesh