Re: [PATCH v6] serial: rewrite pxa2xx-uart to use 8250_core

[Robert Jarzmik]

Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx> writes:

> On Thu, Dec 24, 2015 at 06:15:14PM +0300, Sergei Ianovich wrote:
>> pxa2xx-uart was a separate uart platform driver. It was declaring
>> the same device names and numbers as 8250 driver. As a result,
>> it was impossible to use 8250 driver on PXA SoCs.
>> 
>> Upon closer examination pxa2xx-uart turned out to be a clone of
>> 8250_core driver.
>> 
>> Workaround for Erratum #19 according to Marvel(R) PXA270M Processor
>> Specification Update (April 19, 2010) is dropped. 8250_core reads
>> from FIFO immediately after checking DR bit in LSR.
>> 
>> The patch leaves the original SERIAL_PXA driver around. The original
>> driver is just marked DEPRECATED in Kconfig and C source. When
>> the original driver is considered safe to remove, no changes
>> to SERIAL_8250 will be necessary.
>> 
>> Compiling SERIAL_8250_CONSOLE and SERIAL_PXA_CONSOLE even without
>> SERIAL_8250_PXA breaks console for SERIAL_PXA. For this reasons, the new
>> and the original drivers are made mutually exclusive.
>> 
>> Signed-off-by: Sergei Ianovich <ynvich@xxxxxxxxx>
>> CC: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
>
> Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Tested-by: Robert Jarzmik <robert.jarzmik@xxxxxxx>

The tests were done on lubbock(pxa25x), mainstone(pxa27x) and zylonite(pxa3xx)
boards.

I don't expect any breakage in PXA architecture. There might be issues with :
 - arch/arm/mach-pxa/capc7117.c
 - arch/arm/mach-pxa/viper.c
  -arch/arm/mach-pxa/zeus.c (very small probability for this one)
The mitigation plan if any concern arises is to fallback on the
CONFIG_SERIAL_PXA configuration.

I find a bit misleading this chunk, but I'm not very good at KConfig :
 config SERIAL_PXA
-       bool "PXA serial port support"
+       bool "PXA serial port support (DEPRECATED)"
        depends on ARCH_PXA || ARCH_MMP
        select SERIAL_CORE
+       select SERIAL_8250_PXA if SERIAL_8250=y
+       select SERIAL_PXA_NON8250 if !SERIAL_8250=y

What bothers me a bit is that selecting this option has a different effect
whether SERIAL_8250 is set or not. Somebody selecting the deprecated option
obviously wants the old driver, but will be provided the new one if his config
has SERIAL_8250 set. Maybe someone else can comment on this ...

This apart, from pxa perspective, it's good to go.

Cheers.

-- 
Robert
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