Re: [RFC] mmc: add OMAP driver

[Russell King <rmk+lkml@arm.linux.org.uk>]

One additional comment on the patch which I missed, and has shown to
be a related cause of problems on a different host controller...

On Thu, Feb 16, 2006 at 10:27:22AM -0400, Carlos Aguiar wrote:
> +static inline void set_data_timeout(struct mmc_omap_host *host, struct mmc_request *req)
> +{
> +	int timeout;
> +	u16 reg;
> +
> +	/* Convert ns to clock cycles by assuming 20MHz frequency
> +	 * 1 cycle at 20MHz = 500 ns
> +	 */
> +	timeout = req->data->timeout_clks + req->data->timeout_ns / 500;
> +
> +	/* Some cards require more time to do at least the first read operation */
> +	timeout = timeout << 4;

This is a hack because you got your calculation above wrong.  If you
assume a fast clock, the timeout will be too slow for a slower clock.
If you do the calculation correctly and you won't need such hacks.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core