[U-Boot] [PATCH v2] spi: omap3: Fix timeout handling

[Jagan Teki]

On 7 April 2015 at 05:55, Tom Rini <trini at konsulko.com> wrote:
> On Wed, Apr 01, 2015 at 04:21:50PM +0100, Andy Pont wrote:
>> Hi David,
>>
>> <snipped for brevity>
>>
>> >     for (i = 0; i < len; i++) {
>> >             /* wait till TX register is empty (TXS == 1) */
>> > +           start = get_timer(0);
>> >             while (!(readl(&ds->regs->channel[ds->slave.cs].chstat) &
>> >                      OMAP3_MCSPI_CHSTAT_TXS)) {
>> > -                   if (--timeout <= 0) {
>> > +                   if (get_timer(start) > SPI_WAIT_TIMEOUT) {
>> >                             printf("SPI TXS timed out, status=0x%08x\n",
>> >                                    readl(&ds->regs->channel[ds-
>> > >slave.cs].chstat));
>> >                             return -1;
>>
>> I have a couple of questions...
>>
>> Firstly, when in SPL is there access to the get_timer() function?
>
> We call timer_init() from board_init_r() in SPL, prior to diving down
> into loading (or checking for Falcon vs Regular) so this is safe.
>
>> Secondly, when using Falcon mode to load Linux directly from SPI (Falcon
>> mode) then we want to maximise the throughput and save every CPU cycle we
>> possibly can.  Adding yet another function call into the for loop and hence
>> calling it a couple of million times seems, on the face of it, like it is
>> going to slow things down.
>
> I'd like to see measurements to prove me wrong but this both seems like
> a bad idea (optimizing by being incorrect, this gives us a correct
> timeout check like other drivers do) and really unlikely I would think
> to be noticable.  Since we'll be doing the same code-paths in both
> regular and SPL, trying to time things (by loading a big file) would be
> easy enough I think.  Thanks!

Ping

thanks!
-- 
Jagan.