Re: SPI: Add SPI driver for most known i.MX SoCs

[Julien Boibessot <julien.boibessot-GANU6spQydw@public.gmane.org>]

Hi Sascha,

I finally had some time to test your new unified SPI driver on my i.MX27 
platform...
It's a good idea to have a common SPI driver for all MXs but I have two 
remarks:

Sascha Hauer a écrit :
> While there already is a SPI driver for i.MX1 in the tree there are
> good reasons to replace it:
>
> - The inkernel driver implements a full blown SPI driver, but
>   the hardware can be fully supported using a bitbang driver.
>   This greatly reduces the size and complexity of the driver.
>   
I don't know yet if it's related to bitbang but I would say that your 
driver is 2x slowier that current inkernel one. We (armadeus) have i.MXL 
and i.MX27 boards with ADC, Touchscreen and CAN bus on SPI and saw a 
lost of performance with your driver (when fast successive SPI transfers 
are needed). You probably won't notice it if you only have a Freescale's 
power chip or an EEPROM connected to your SPI bus.

Sorry but I didn't had time yet to investigate more :-(.

I know that I can't have the official Linux kernel suited for my 
particular needs (;-) ), so what would be the things to do to improve 
your driver performances ?
> - The DMA API of the durrent driver is broken for arch-mx1 (as opposed
>   to arch-imx) and nobody cared to fix it yet.
>   
Will your driver use DMA in a near future ?

Regards,
Julien

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