[U-Boot] [PATCH] S5P: new spi gpio bitbang driver

[Mike Frysinger]

On Wednesday, September 15, 2010 01:15:08 Donghwa Lee wrote:
>  On Tuesday, September 14, 2010 20:48:11 Mike Frysinger wrote:
> > On Tuesday, September 14, 2010 03:38:11 Donghwa Lee wrote:
> >> This patch adds basic support for spi mode 0~3 by control gpio bitbang
> >> in S5P. Original name of this patch was "support spi gpio driver by
> >> control gpio bitbang". But, it had arch-specific features, S5P, so
> >> changed to this name.
> > 
> > so why arent you implementing this with the common spi API ?  then any of
> > the code in the tree would be able to use this spi driver without having
> > to change to your arch-specific API.
> 
> I think common spi API is not appropriate for S5P arch. For example,
> arch-S5P gpio framework consists of many gpio bank structure, and gpio
> number. From here, gpio bank structures are groups of many gpio pin and
> gpio number indicates specific gpio pin of gpio bank group. To control any
> gpio pin in arch S5P, must know about gpio bank and its specific number.
> But, existing spi API is different from avobe.
> For example, spi_setup_slave() function, consists of 4 function parameter,
> bus, cs, max_hz and mode. bus and cs is specific gpio number that not gpio
> bank group. so I think it is hard to control gpio without modifying API
> format.

i dont see how this matters.  implement the common gpio api and handle the 
binding of a unique number to specific bank/pin there.  then the spi/gpio 
layer need not care about how gpios are implement on any arch.

the Blackfin port already does this.  each variant has a different number of 
gpio ports with a different number of pins in each bank.  you can see in 
arch/blackfin/include/asm/mach-*/gpio.h how we then normalize the banks/pins 
into numbers from 0 to <gpio max for that arch>.  then spi layer simply says 
"give me gpio 12" and the gpio layer takes care of the port/pin layer.
-mike
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