Re: [PATCH v5 15/17] dt-bindings: qca7000: append UART interface to binding

[Stefan Wahren]

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@xxxxx>:
>>
>>> 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@xxxxxxxx>
>>>>> ---
>>>>>  .../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@80014000 {
>>>>>  		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?

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

Regards
Stefan