Re: [PATCH] spi: rockchip: Disable local irq when pio write out of interrupt service

[Jon Lin]

On 2022/6/17 19:45, Mark Brown wrote:
> On Fri, Jun 17, 2022 at 02:24:10PM +0800, Jon Lin wrote:
> > On 2022/6/13 20:37, Mark Brown wrote:
> > > On Mon, Jun 13, 2022 at 05:27:44PM +0800, Jon Lin wrote:
>
> > > > +	spin_unlock_irqrestore(&rs->lock, flags);
>
> > > So this is effectively just disabling interrupts during PIO, there's no
> > > other users of the lock which is rather heavyweight.  What's the actual
> > > issue here?  We should also have something saying what's going on in the
> > > code since right now the lock just looks redundant.
>
> > For lock: In order to avoid special situations, such as when the CPU
> > frequency drops to close to the IO rate, the water line interrupt is
> > triggered during FIFO filling (triggered by other CPUs), resulting in
> > critical resources still not being protected in place. For local IRQ
>
> So essentially we're so slow in filling the FIFO when starting a
> transfer that the interrupt triggers in the middle of the initial FIFO
> fill?  Something that tricky *really* needs a comment adding.
>
> Ideally we'd just leave the interrupt masked until the FIFO is filled
> though, looking at the driver I see that there is an interrupt mask
> register which seems to have some level of masking available and I do
> note that in rockchip_spi_prepare_irq() we unmask interrupts before we
> start filling the FIFO rather than afterwards.  Would reversing the
> unmask order there address the issue more cleanly?

This idea is workable, and it's more efficient than previous code, So I 
send a new commit:
https://patchwork.kernel.org/project/spi-devel-general/patch/20220617124251.5051-1-jon.lin@xxxxxxxxxxxxxx/
> > disable: Turning off the local interrupt is mainly to prevent the CPU
> > schedule from being interrupted when filling FIFO.
>
> If it were just this then there's preempt_disable(), but what's the
> problem with being preempted during the FIFO fill?

I think