linux-kernel - Re: [PATCH 01/10] spi: spi-axi-spi-engine: remove usage of delay

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Date:   Wed, 10 Mar 2021 09:16:51 +0200
From:   Alexandru Ardelean <aardelean@...iqon.com>
To:     Lars-Peter Clausen <lars@...afoo.de>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        greybus-dev@...ts.linaro.org, devel@...verdev.osuosl.org,
        linux-tegra@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        broonie@...nel.org, gregkh@...uxfoundation.org, elder@...nel.org,
        johan@...nel.org, vireshk@...nel.org, rmfrfs@...il.com,
        f.fainelli@...il.com, ldewangan@...dia.com,
        thierry.reding@...il.com, jonathanh@...dia.com, linux@...iqon.com
Subject: Re: [PATCH 01/10] spi: spi-axi-spi-engine: remove usage of delay_usecs

On Mon, 8 Mar 2021 at 18:42, Lars-Peter Clausen <lars@...afoo.de> wrote:
>
> On 3/8/21 3:54 PM, Alexandru Ardelean wrote:
> > The 'delay_usecs' field was handled for backwards compatibility in case
> > there were some users that still configured SPI delay transfers with
> > this field.
> >
> > They should all be removed by now.
> >
> > Signed-off-by: Alexandru Ardelean <aardelean@...iqon.com>
> > ---
> >   drivers/spi/spi-axi-spi-engine.c | 12 ++++--------
> >   1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/spi/spi-axi-spi-engine.c b/drivers/spi/spi-axi-spi-engine.c
> > index af86e6d6e16b..80c3e38f5c1b 100644
> > --- a/drivers/spi/spi-axi-spi-engine.c
> > +++ b/drivers/spi/spi-axi-spi-engine.c
> > @@ -170,14 +170,10 @@ static void spi_engine_gen_sleep(struct spi_engine_program *p, bool dry,
> >       unsigned int t;
> >       int delay;
> >
> > -     if (xfer->delay_usecs) {
> > -             delay = xfer->delay_usecs;
> > -     } else {
> > -             delay = spi_delay_to_ns(&xfer->delay, xfer);
> > -             if (delay < 0)
> > -                     return;
> > -             delay /= 1000;
> > -     }
> > +     delay = spi_delay_to_ns(&xfer->delay, xfer);
> > +     if (delay < 0)
> > +             return;
>
> Bit of a nit, but this could be `delay <= 0` and then drop the check for
> `delay == 0` below.

hmm, that's a bit debatable, because the `delay == 0` check comes
after `delay /= 1000` ;
to do what you're suggesting, it would probably need a
DIV_ROUND_UP(delay, 1000) to make sure that even sub-microsecond
delays don't become zero;

if you're acking this suggestion i'll implement it;
i'll wait a few more days to see if there are any other acks or
complaints on the set before sending a V2;

btw: this new spi_delay struct supports delays in microseconds,
nanoseconds and clock cycles;
at some point it may be interesting to use a
`spi_delay_to_clk_cycles()` for this driver and other similar;

>
> > +     delay /= 1000;
> >
> >       if (delay == 0)
> >               return;
>
>