linux-kernel - Re: [v5 2/2] dt-bindings: mtd: Add Cadence NAND controller driver

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Date:   Fri, 13 Sep 2019 15:41:22 +0100
From:   Piotr Sroka <piotrs@...ence.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        <devicetree@...r.kernel.org>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Richard Weinberger <richard@....at>,
        Marek Vasut <marek.vasut@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-mtd@...ts.infradead.org>,
        BrianNorris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Kazuhiro Kasai <kasai.kazuhiro@...ionext.com>
Subject: Re: [v5 2/2] dt-bindings: mtd: Add Cadence NAND controller driver

The 09/13/2019 14:49, Miquel Raynal wrote:
>EXTERNAL MAIL
>
>
>Hi Piotr,
>
>Piotr Sroka <piotrs@...ence.com> wrote on Wed, 11 Sep 2019 16:04:24
>+0100:
>
>> Hi Miquel
>>
>> The 08/30/2019 11:46, Miquel Raynal wrote:
>> >EXTERNAL MAIL
>> >
>> >
>> >Hi Piotr,
>> >
>> >Piotr Sroka <piotrs@...ence.com> wrote on Thu, 25 Jul 2019 15:59:55
>> >+0100:
>> >
>> >> Document the bindings used by Cadence NAND controller driver
>> >>
>> >> Signed-off-by: Piotr Sroka <piotrs@...ence.com>
>> >> ---
>> >> Changes for v5:
>> >> - replace "_" by "-" in all properties
>> >> - change compatible name from cdns,hpnfc to cdns,hp-nfc
>> >> Changes for v4:
>> >> - add commit message
>> >> Changes for v3:
>> >> - add unit suffix for board_delay
>> >> - move child description to proper place
>> >> - remove prefix cadence_ for reg and sdma fields
>> >> Changes for v2:
>> >> - remove chip dependends parameters from dts bindings
>> >> - add names for register ranges in dts bindings
>> >> - add generic bindings to describe NAND chip representation
>> >> ---
>> >>  .../bindings/mtd/cadence-nand-controller.txt       | 50 ++++++++++++++++++++++
>> >>  1 file changed, 50 insertions(+)
>> >>  create mode 100644 Documentation/devicetree/bindings/mtd/cadence-nand-controller.txt
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/mtd/cadence-nand-controller.txt b/Documentation/devicetree/bindings/mtd/cadence-nand-controller.txt
>> >> new file mode 100644
>> >> index 000000000000..423547a3f993
>> >> --- /dev/null
>> >> +++ b/Documentation/devicetree/bindings/mtd/cadence-nand-controller.txt
>> >> @@ -0,0 +1,50 @@
>> >> +* Cadence NAND controller
>> >> +
>> >> +Required properties:
>> >> +  - compatible : "cdns,hp-nfc"
>> >> +  - reg : Contains two entries, each of which is a tuple consisting of a
>> >> +	  physical address and length. The first entry is the address and
>> >> +	  length of the controller register set. The second entry is the
>> >> +	  address and length of the Slave DMA data port.
>> >> +  - reg-names: should contain "reg" and "sdma"
>> >> +  - interrupts : The interrupt number.
>> >> +  - clocks: phandle of the controller core clock (nf_clk).
>> >> +
>> >> +Optional properties:
>> >> +  - dmas: shall reference DMA channel associated to the NAND controller
>> >> +  - cdns,board-delay-ps : Estimated Board delay. The value includes the total
>> >> +    round trip delay for the signals and is used for deciding on values
>> >> +    associated with data read capture. The example formula for SDR mode is
>> >> +    the following:
>> >> +    board delay = RE#PAD delay + PCB trace to device + PCB trace from device
>> >> +    + DQ PAD delay
>> >> +
>> >> +Child nodes represent the available NAND chips.
>> >> +
>> >> +Required properties of NAND chips:
>> >> +  - reg: shall contain the native Chip Select ids from 0 to max supported by
>> >> +    the cadence nand flash controller
>> >> +
>> >> +
>> >> +See Documentation/devicetree/bindings/mtd/nand.txt for more details on
>> >> +generic bindings.
>> >> +
>> >> +Example:
>> >> +
>> >> +nand_controller: nand-controller @60000000 {
>> >> +	  compatible = "cdns,hp-nfc";
>> >> +	  reg = <0x60000000 0x10000>, <0x80000000 0x10000>;
>> >> +	  reg-names = "reg", "sdma";
>> >> +	  clocks = <&nf_clk>;
>> >> +	  cdns,board-delay-ps = <4830>;
>> >
>> >Are you sure you want to export this to the user? Not sure it is easily
>> >understandable and tunable... I'm not against but I would have troubles
>> >tuning it myself, unless using the documented value. Maybe you should
>> >explain more how to derive it?
>> I need to export this parameter somehow. The default value may not be
>> valid for other platforms. This value depends on platform, and may be different on different SoCs. So I think the DTS is the best place to put such configuration
>> parameter.
>
>What about a different compatible if it depends on the SoC?
I considered it but this dealy consists of PADs delay and PCB trace
delay. PAD delays are SoC dependent. Unfortunatelly PCB delay not.
What can I do I can split it on two delays, PAD_delay and trace_delay.
Then handle PAD_delay by compatible and trace_delay by dts. But I am not
sure whether it changes anythig. Still a delay need to passed by dts.
>
>This way you can retrieve a different driver data structure and avoid
>the pain for the user.

>
>Thanks,
>Miquèl


Thanks
Piotr