Message-ID: <CAL_JsqKmuRJbuBy8zdjXgL6Y8A0zGT5nMpr2g=H7VgfTzAmOoA@mail.gmail.com>
Date:   Fri, 19 May 2017 07:37:44 -0500
From:   Rob Herring <robh@...nel.org>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Jakub Kicinski <kubakici@...pl>,
        Michael Heimpold <mhei@...mpold.de>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 15/17] dt-bindings: qca7000: append UART interface to binding

On Fri, May 19, 2017 at 2:13 AM, Stefan Wahren <stefan.wahren@...e.com> wrote:
> Hi Rob,
>
> Am 12.05.2017 um 08:43 schrieb Jakub Kicinski:
>> On Fri, 12 May 2017 06:15:52 +0000, Michael Heimpold wrote:
>>> Hi,
>>>
>>> Zitat von Jakub Kicinski <kubakici@...pl>:
>>>
>>>> On Thu, 11 May 2017 21:12:22 +0200, Michael Heimpold wrote:
>>>>> Am Mittwoch, 10. Mai 2017, 10:53:26 CEST schrieb Stefan Wahren:
>>>>>> This merges the serdev binding for the QCA7000 UART driver (Ethernet over
>>>>>> UART) into the existing document.
>>>>>>
>>>>>> Signed-off-by: Stefan Wahren <stefan.wahren@...e.com>
>>>>>> ---
>>>>>>  .../devicetree/bindings/net/qca-qca7000.txt        | 32
>>>>>> ++++++++++++++++++++++ 1 file changed, 32 insertions(+)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/net/qca-qca7000.txt
>>>>>> b/Documentation/devicetree/bindings/net/qca-qca7000.txt index
>>>>>> a37f656..08364c3 100644
>>>>>> --- a/Documentation/devicetree/bindings/net/qca-qca7000.txt
>>>>>> +++ b/Documentation/devicetree/bindings/net/qca-qca7000.txt
>>>>>> @@ -54,3 +54,35 @@ ssp2: spi@...14000 {
>>>>>>           local-mac-address = [ A0 B0 C0 D0 E0 F0 ];
>>>>>>   };
>>>>>>  };
>>>>>> +
>>>>>> +(b) Ethernet over UART
>>>>>> +
>>>>>> +In order to use the QCA7000 as UART slave it must be defined as
>>>>> a child of
>>>>>> a +UART master in the device tree. It is possible to preconfigure the UART
>>>>>> +settings of the QCA7000 firmware, but it's not possible to change them
>>>>>> during +runtime.
>>>>>> +
>>>>>> +Required properties:
>>>>>> +- compatible        : Should be "qca,qca7000-uart"
>>>>> I already discussed this with Stefan off-list a little bit, but I would like
>>>>> to bring this to a broader audience: I'm not sure whether the compatible
>>>>> should contain the "-uart" suffix, because the hardware chip is the
>>>>> very same
>>>>> QCA7000 chip which can also be used with SPI protocol.
>>>>> The only difference is the loaded firmware within the chip which can either
>>>>> speak SPI or UART protocol (but not both at the same time - due to shared
>>>>> pins). So the hardware design decides which interface type is used.
>>>>>
>>>>> At the moment, this patch series adds a dedicated driver for the UART
>>>>> protocol, in parallel to the existing SPI driver. So a different compatible
>>>>> string is needed here to match against the new driver.
>>>>>
>>>>> An alternative approach would be to re-use the existing compatible string
>>>>> "qca,qca7000" for both, the SPI and UART protocol, because a "smarter"
>>>>> (combined) driver would detect which protocol to use. For example the driver
>>>>> could check for spi-cpha and/or spi-cpol which are required for SPI
>>>>> protocol:
>>>>> if these exists the driver could assume that SPI must be used, if both are
>>>>> missing then UART protocol should be used.
>>>>> (This way it would not be necessary to check whether the node is a child of
>>>>> a SPI or UART master node - but maybe this is even easier - I don't know)
>>>>>
>>>>> Or in shorter words: my concern is that while "qca7000-uart" describes the
>>>>> hardware, it's too closely coupled to the driver implementation. Having
>>>>> some feedback of the experts would be nice :-)
>>>> I'm no expert, but devices which can do both I2C and SPI are quite
>>>> common, and they usually have the same compatible string for both
>>>> buses.
>>> do you have an example driver at hand? I only found GPIO mcp23s08 driver,
>>> which can handle both I2C and SPI chips, but there are different compatible
>>> strings used to distinguish several chip models.
>> I think drivers/tty/serial/sc16is7xx.c has the same strings, and some
>> Kconfig magic to work when either bus is enabled in .config.
>>
>> Quick grep shows there are couple more potential ones to look at:
>>
>> $ find . -name Kconfig | xargs grep -n 'SPI_MASTER.* I2C'
>> ./drivers/tty/serial/Kconfig:1208:        depends on (SPI_MASTER && !I2C) || I2C
>> ./drivers/mfd/Kconfig:327:    depends on (SPI_MASTER || I2C)
>> ./drivers/iio/dac/Kconfig:10: depends on (SPI_MASTER && I2C!=m) || I2C
>> ./drivers/iio/dac/Kconfig:34: depends on (SPI_MASTER && I2C!=m) || I2C
>> ./drivers/iio/dac/Kconfig:57: depends on (SPI_MASTER && I2C!=m) || I2C
>> ./drivers/gpio/Kconfig:1231:  depends on (SPI_MASTER && !I2C) || I2C
>> $ find . -name Kconfig | xargs grep -n 'I2C.*||.*SPI_MASTER'
>> ./drivers/mfd/Kconfig:1094:   depends on (I2C=y || SPI_MASTER=y)
>> ./drivers/iio/gyro/Kconfig:55:        depends on (I2C || SPI_MASTER)
>> ./drivers/iio/gyro/Kconfig:107:       depends on (I2C || SPI_MASTER) && SYSFS
>> ./drivers/iio/accel/Kconfig:153:      depends on (I2C || SPI_MASTER) && SYSFS
>> ./drivers/iio/pressure/Kconfig:20:    depends on (I2C || SPI_MASTER)
>> ./drivers/iio/pressure/Kconfig:161:   depends on (I2C || SPI_MASTER) && SYSFS
>> ./drivers/iio/magnetometer/Kconfig:118:       depends on (I2C || SPI_MASTER) && SYSFS
>>
>> drivers/mfd/mc13xxx-*.c seems to have the same strings.  The iio/dac drivers
>> don't support DT but do share names.  The MCP GPIO chip you mention indeed has
>> different product names based on the bus it's made for (0 vs s in the middle
>> of the name), so I gather less relevant case?  drivers/iio/pressure/bmp280-*.c
>> has the same strings, if I'm looking correctly... I didn't look at the others.
>
> are you okay with the suggestion to use the compatible "qca,qca7000" for
> both drivers?

I believe I said I was fine either way.

> Should we mark "qca,qca7000-spi" as deprecated?

Yes.

Rob

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