[PATCH 1/2] spi: bcm2835: add spi-bcm2835aux driver for the auxiliar spi1 and spi2

[Stephen Warren]

On 07/11/2015 08:10 PM, Martin Sperl wrote:
> I am on a business-trip right now, so I can not check the mailing list
> that often and my access to a rpi to develop is also limited hence
> the V3 patch set took some time to get out of the door and crossed
> the responses you had sent.
> 
>> On 11.07.2015, at 14:53, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> Hopefully the license of that tar file allows for that. I didn't look.
> Well, I just took the values from the released video driver for those values
> where doe documentation is obviously wrong - essentially clarifying
> the SPI_STAT register on page 25.
> 
>> As mentioned elsewhere, I'd hope all the shared aux register
>> manipulations can be pushed into a shared driver.
> 
> I just found this email after having sent the latest version of the patch
> that makes use of syscon/regmap to serialize access to the
>  bcm2835_AUX_ENABLE register - that is all that it is really needed for.
> 
> From my perspective it seems that a new driver just would produce
> more code (to maintain) for something that the syscon driver already
> provides. If someone starts to enable aux-uart, then it could go with
> a new framework, but that is still more code that needs to get maintained
> than just using syscon as that "shared" driver.
> 
> As for hardcoded ids, that may be the case, but I just wanted to keep
> Device tree as minimal as necessary...
> If we get to that situation then we can easily move that to some
> other logic...
> 
> Finally with regards to interrupts: these are shared anyway so I
> wonder why we would want to write an extra irq chip driver when
> it works as is anyway.
> 
> If someone thinks that is of a performance advantage then this
> extra layer of indirection could get written and we would only need
> to change the device-tree to use the new irq vectors instead.
> 
> But we are really only talking about 2 drivers and 3 interrupt sources.

I don't care so much about the internal code details; anything there can
be trivially changed. But please do make sure the DT correctly
represents the HW by:

* Having a separate DT node for each HW block (SPI controller, UART, and
any shared interrupt mux/demux/controller/...)

* If e.g. the SPI controller driver is going to need to manipulate the
"shared interrupt mux/demux/controller/...", there should be a phandle
from the SPI controller node to the "shared interrupt
mux/demux/controller/..." node, rather than listing the shared registers
in each "client"'s reg property.