iMX28 SPI max clock rate

Matt_ — Wed, 24 Apr 2013 16:22:06 GMT

Hello,

linux-2.6.35.3\drivers\spi\spi_mxs.c tries to set the maximum clock rate using the lines

rate = 1000 * ss->speed_khz / ss->divider / hz;

__raw_writel(BF_SSP_TIMING_CLOCK_DIVIDE(ss->divider) |

BF_SSP_TIMING_CLOCK_RATE(rate - 1),

ss->regs + HW_SSP_TIMING);

However this should round up the calculated rate variable otherwise the clock is set beyond the rate requested, e.g.

ss->speed_khz = 24000

ss->divider = 2

hz = 7000000 (requesting max rate of 7MHz)

==> rate = 1 (rounded down from 1.7)

==> SPI clock = 24000000 / (2 * (1+0)) = 12000000, i.e. 12MHz

This can be fixed in many ways. I did

if ((1000 * ss->speed_khz) > (rate * ss->divider * hz))

rate++; /* round up */

Matt.

Re: iMX28 SPI max clock rate

GraceH — Tue, 07 May 2013 06:28:46 GMT

Hi Matt,

Your change is correct. Thanks for your correction.

Grace