[U-Boot-Users] [PATCH v2] spi: Kill spi_chipsel table and introduce spi_setup()

[Haavard Skinnemoen]

On Tue, 5 Feb 2008 23:34:46 -0500
Mike Frysinger <vapier at gentoo.org> wrote:

> so the new SPI interface has this API:
>  - void spi_init(void);
>  - int spi_setup(int cs, unsigned int max_hz, unsigned int mode);
>  - int spi_xfer(int cs, int bitlen, uchar *dout, uchar *din);
>  - int spi_cs_is_valid(int cs);
>  - void spi_cs_activate(int cs);
>  - void spi_cs_deactivate(int cs);

Yes, or at least that's the current API + my proposed patch.

> there isnt a function to pair up with spi_setup() ?  for example, the normal 
> communication flow with a SPI flash:
>  - spi_setup - turn on SPI
>  - spi_cs_activate - assert CS
>  - spi_xfer -
> 	- op code (read/write/erase)
> 	- address
> 	- actual block data
>  - spi_cs_deactivate - deassert CS
>  - ??? - turn off SPI

Right. I thought of spi_setup() more as a function that needs to be
called one time per slave to set up communications parameters, not
really for turning the SPI on as such.

But perhaps it would make sense to combine those two functions. How
about we turn it into

/* Set slave-specific parameters and enable SPI */
int spi_claim_bus(int cs, unsigned int max_hz, unsigned int mode);

/* Disable SPI */
void spi_release_bus(int cs);

The claim/release naming also makes it clear that the SPI device driver
has exclusive access to the bus between those two calls.

> you dont want to have the deactivate func to turn off SPI in case you need to 
> toggle the CS during communication ... some SPI peripherals have undefined 
> (floating) behavior with pins when it is actually turned off which is bad 
> mojo ...

Sure, I didn't mean to suggest that spi_cs_deactivate() should turn off
the whole SPI controller.

Btw, the master driver is currently controlling the chip selects from
spi_xfer(). I suspect we need to give clients greater control of the
chip selects eventually.

> also, what's the deal with spi_xfer() taking a length in # of bits ?  is it 
> realistic to transmit anything less tan 8 bits ?  the Linux kernel driver 
> does not support this, so it cant be a big need ...

I don't know. That's unchanged from the original API. But I certainly
wouldn't object if we turned it into a length in bytes.

Haavard