[U-Boot-Users] [PATCH v2 1/3] New i.MX31 SPI driver

[Guennadi Liakhovetski]

On Thu, 8 May 2008, Haavard Skinnemoen wrote:

> > I thought, like (pseudocode)
> > 
> > static struct spi_host busses[SPI_BUSSES];
> > 
> > struct spi_slave *spi_init()
> > {
> > 	list_for_each_entry(slave, &busses[bus].slaves, list) {
> > 		if (slave->device == device)
> > 			return (struct spi_slave *)-EBUSY;
> > 	}
> > 	slave = malloc();
> > 	slave->bus = bus;
> > 	slave->device = device;
> > 	ret = busses[bus].init(slave);
> > 	if (ret) {
> > 		free(slave);
> > 		return (struct spi_slave *)ret;
> > 	}
> > 	return slave;
> > }
> >
> > int spi_xfer()
> > {
> > 	list_for_each_entry(ix, &busses[bus].slaves, list) {
> > 		if (ix == slave)
> > 			break;
> > 	}
> > 	if (ix != slave)
> > 		return -EINVAL;
> > 
> > 	if (slave->bus->busy)
> > 		return -EBUSY;
> > 
> > 	return slave->bus->xfer();
> > }
> 
> I was thinking about something much simpler:
> 
> struct spi_slave *spi_init_slave(bus, cs, max_hz, mode)
> {
> 	slave = malloc();
> 	slave->regs = get_spi_controller_base_address(bus);
> 	slave->mode_reg = get_suitable_settings_for(cs, max_hz, mode);
> 	return slave;
> }
> 
> int spi_xfer(slave, ...)
> {
> 	__raw_writel(slave->mode_reg, slave->regs + SPI_MR);
> 	if (flags & SPI_XFER_BEGIN)
> 		assert_chip_select();
> 
> 	do_the_actual_spi_transfer();
> 
> 	if (flags & SPI_XFER_END)
> 		deassert_chip_select();
> 
> 	return whatever;
> }
> 
> Of course, your solution will work with multiple, different SPI
> controllers while mine won't, but is that really necessary?
> 
> Your solution comes with more error checking as well, which might be a
> good thing, but since it comes with a cost of additional memory and
> flash footprint, I think it should be optional. Maybe we could provide
> some library functions to simplify the drivers that want this?

I see. Well, I don't have a strong preference. So, either we need more 
votes, or the one who implements it decides:-)

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.

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