[PATCH 06/10 V2] spi: Add SPI driver for mx233/mx28

On Fri, Aug 3, 2012 at 10:38 AM, Thomas Petazzoni
[off-list ref] wrote:

It sounds really strange to manipulate WAIT_FOR_CMD and WAIT_FOR_IRQ
bits to adjust the chip select, and when reading the driver, it seemed
suspicious to me. After going through the datasheet, indeed those bits
are the appropriate one to select between the SS0, SS1 and SS2 chip
selects, but I find the code not really obvious. Would it be possible
to make it more obvious either by adding or comment or doing something
like:

/* Should be put in some header file */
#define BM_SSP_CTRL0_SPI_CS_BITS (20)

+static void mxs_spi_set_cs(struct mxs_spi *spi, unsigned cs)
+{
+       struct mxs_ssp *ssp = &spi->ssp;
+
+       writel(0x3 << BM_SSP_CTRL0_SPI_CS_BITS,
+              ssp->base + HW_SSP_CTRL0 + STMP_OFFSET_REG_CLR);
+       writel(cs,
+              ssp->base + HW_SSP_CTRL0 + STMP_OFFSET_REG_SET);
+}

I agree with Thomas.

In U-boot I did the following in order to be able to select the
different chip selects:
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=148ca64f327a89ef77e84756f5d351af33e59b64

Thanks,

Fabio Estevam