sata_link_debounce: Delays boot by 100 ms, hard coded as minimal debounce duration

[Paul Menzel <pmenzel@xxxxxxxxxxxxx>]

Dear Linux folks,


Trying to decrease Linux’ overall boot time, tracing 
`sata_link_resume()` with ftrace, it calls  `sata_link_debounce()` also 
in `drivers/ata/libata-sata.c`

    if ((rc = sata_link_debounce(link, params, deadline)))
    		return rc;

which runs a while loop, and takes the parameters defined in arrays at 
the top of the file.

    /* debounce timing parameters in msecs { interval, duration, 
timeout } */
    const unsigned long sata_deb_timing_normal[]            = {   5, 
100, 2000 };
    EXPORT_SYMBOL_GPL(sata_deb_timing_normal);
    const unsigned long sata_deb_timing_hotplug[]           = {  25, 
500, 2000 };
    EXPORT_SYMBOL_GPL(sata_deb_timing_hotplug);
    const unsigned long sata_deb_timing_long[]              = { 100, 
2000, 5000 };
    EXPORT_SYMBOL_GPL(sata_deb_timing_long);

const unsigned long sata_deb_timing_normal[]            = {   5,  100, 
2000 };

So the duration is set to 100 ms, which is quite a long time on current 
systems. At least on the Asus F2A85-M PRO that does not seem to be 
necessary. The motivation for adding these delays seems to be again 
broken controllers:

> Make sure SStatus of @link reaches stable state, determined by
> holding the same value where DET is not 1 for @duration polled every
> @interval, before @timeout.  Timeout constraints the beginning of the
> stable state.  Because DET gets stuck at 1 on some controllers after
> hot unplugging, this functions waits until timeout then returns 0 if
> DET is stable at 1.

As I neither know the SATA standard nor the Linux code well, do you have 
a suggestion how to improve that on controllers not needing such a long 
delay? Make the duration value configurable on Linux’ command line?


Kind regards,

Paul