lkml.org 
[lkml]   [2022]   [Jun]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] spi: rockchip: Disable local irq when pio write out of interrupt service
From


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@rock-chips.com/
>
>> 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

\
 
 \ /
  Last update: 2022-06-17 14:47    [W:0.049 / U:0.616 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site