Re: [PATCH v3 11/11] spi: opportunistically skip ctlr->cur_msg_completion

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Tue, Jun 21, 2022 at 8:16 AM David Jander <david@xxxxxxxxxxx> wrote:
>
> There are only a few drivers that do not call
> spi_finalize_current_message() in the context of transfer_one_message(),
> and even for those cases the completion ctlr->cur_msg_completion is not
> needed always. The calls to complete() and wait_for_completion() each
> take a spin-lock, which is costly. This patch makes it possible to avoid
> those calls in the big majority of cases, by introducing two flags that
> with the help of ordering via barriers can avoid using the completion
> safely. In case of a race with the context calling
> spi_finalize_current_message(), the scheme errs on the safe side and takes
> the completion.
> The impact of this patch is worth the effort: On a i.MX8MM SoC, the time
> the SPI bus is idle between two consecutive calls to spi_sync(), is
> reduced from 19.6us to 16.8us... roughly 15%.

...

> +       smp_wmb(); /* make these available to spi_finalize_current_message */

spi_finalize_current_message()

...

> +               smp_mb(); /* see spi_finalize_current_message()... */

Be consistent with capitalization of one-liner comments, see below.

...

> +       smp_mb(); /* See __spi_pump_transfer_message()... */

^^^

This comment (and any other) applies to the entire series where it makes sense.

-- 
With Best Regards,
Andy Shevchenko