Hi,
On Thu, May 06, 2010 at 04:13:41PM +0200, Alexander Stein wrote:
I can't say much about actual transfer rates. But i noticed a real slowdown when the filesystem buffer is about to be flushed. We are using a COldfire 5484 and AFAIK there is no DMA for SPI, at least we don't use it.
I used M54451EVB/M54455EVB as a starting point, both use eDMA for SPI by default. Sorry, don't know about MCF547x/548x.
Things are clearing up now: as far as I could see, there are no real timing-relevant things changed in mmc_spi code, BUT the underlying SPI driver is crucial.
Setting the same default timing values found in mcf5445x-devices.c in U-Boot (CONFIG_SYS_DSPI_CTAR0), I can degrade the performance of MMC-SPI in U-Boot by a factor of 3, approximately. However, setting the fast default values from U-Boot in the linux kernel (mcf5445x-devices.c) makes things even worse there, too.
After all, I am sure now it is only the SPI part I have to investigate further, most probably concerning latency between transfers.
Thanks for the comments and sorry for the noise!
Best regards, Wolfgang