Re: [PATCH 1/3] spi: xilinx: Detect stall with Unknown commands

[Ricardo Ribalda Delgado <ricardo.ribalda-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Mark


On Wed, Nov 22, 2017 at 12:12 PM, Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> On Tue, Nov 21, 2017 at 10:09:02AM +0100, Ricardo Ribalda Delgado wrote:
>
>> +             stalled = 10;
>>               while (rx_words) {
>> +                     if (rx_words == n_words && !(stalled--) &&
>> +                         !(sr & XSPI_SR_TX_EMPTY_MASK) &&
>> +                         (sr & XSPI_SR_RX_EMPTY_MASK)) {
>
> 10 seems like a small number for what is essentially just a busy spin -
> are we sure that we won't reasonably hit a case where the CPU is
> sufficiently fast and the bus sufficiently slow we falsely detect a
> stall?  Where did this number come from?

This code is executed after all the data has been pushed to the out
fifo. Since we are not inhibitng tx, the moment the empty mask is
evaluated,  at least one byte should be out.

After 1 day of use I have been able to locate one event when stalled
was two. So 10 is very conservative number.

In other words: 10 is one order of magnitude bigger than the worst
measured case.

Thanks for your review :)


-- 
Ricardo Ribalda
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