spibus access serialization

[Warner Losh]

On Sep 2, 2012, at 6:37 AM, Luiz Otavio O Souza wrote:

> Hi,
> 
> I've some embedded systems with spi devices that share the same spibus and because of that i'm working to get some kind of access serialization on spibus and also protection to devices which need a series of spi transfers to achieve some goal.
> 
> The SPI usage (with all the patches applied) goes like this:
> 
> /* Wait until the spibus is free. When free, acquire the bus and select the device */
> SPIBUS_ACQUIRE_BUS(spibus, device);

Does it do this with a sleep?

> /* Program the CPLD to read data from NAND */
> SPIBUS_TRANSFER(spibus, device, &cmd);
> 
> /* Read 'n' bytes from CPLD */
> SPIBUS_TRANSFER(spibus, device, &cmd);
> 
> /* Release the spibus and deselect the device */
> SPIBUS_RELEASE_BUS(spibus, device);
> 
> While today everything is done inside SPIBUS_TRANSFER().
> 
> The patch spibus-01.diff adds the bus methods and the default methods.
> 
> The spibus-02-devices.diff adds the needed glue to all spi devices (dev/flash/at45d.c, dev/flash/mx25l.c, arm/lpc/ssd1289.c, mips/atheros/pcf2123_rtc.c). As the default methods are just nops, there are no functional changes.
> 
> On spibus-03-controllers.diff we finally add the serialization methods to spi controllers (mips/atheros/ar71xx_spi.c and arm/lpc/lpc_spi.c) and change the device CS to happen on bus acquire and release and not on start and end of each transfer.
> 
> The spi controller on arm/at91/at91_spi.c wasn't changed because looks like it will be need to move the device CS control from the controller and use it as a GPIO pin. I need to read more of at91 code before i can suggest some change there. Until there it will work just as now (no serialization and selecting/deselecting the device within each transfer).

The at91_spi controller controls which CS line is asserted.  So long as you don't change the bits in the registers, it will stay asserted.  I think it can fit with this scheme.  I'll have to take a closer look.  All my AT91 devices have only one chip on the spi bus.

> Comments ?

I like the idea....  I'll review the code in more detail to see if I see any gotchas in it.

Not sure why we need so many different flash modules, but that's a different issue.

> Thanks,
> Luiz
> 
> 
> 
> <spibus-01.diff><spibus-02-devices.diff><spibus-03-controllers.diff>_______________________________________________
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