Hi Rob,

Am 12.05.2017 um 08:43 schrieb Jakub Kicinski:

On Fri, 12 May 2017 06:15:52 +0000, Michael Heimpold wrote:

quoted

Hi,

Zitat von Jakub Kicinski [off-list ref]:

quoted

On Thu, 11 May 2017 21:12:22 +0200, Michael Heimpold wrote:  

quoted

Am Mittwoch, 10. Mai 2017, 10:53:26 CEST schrieb Stefan Wahren:  

quoted

This merges the serdev binding for the QCA7000 UART driver (Ethernet over
UART) into the existing document.

Signed-off-by: Stefan Wahren <redacted>
---
 .../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  

quoted

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
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