Re: [PATCH v2 1/1] dmaengine: switchtec-dma: Introduce Switchtec DMA engine PCI driver

[Kelvin.Cao]

On Thu, 2023-04-13 at 22:50 -0700, Christoph Hellwig wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you >
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> > 
> > On Thu, Apr 13, 2023 at 10:40:41PM +0000, >
> > Kelvin.Cao@xxxxxxxxxxxxx wrote:
> > > > > > > > Why is the lock needed while reading the status and
> > > > > > > > waiting
> > > > > > > > for it with long delays?
> > > > There's (low) chance of access to the same ctrl register from
> > > > other
> > > > paths which might change the value of status in an unexpected
> > > > way. > > It
> > > > also prevents the hardware operation from being interrupted
> > > > until > > it
> > > > indicates it has finished by a bit set in the status register.
> > 
> > Well, the lock is obviously required to protecte the reads to the
> > register.  But why do you need to hold the lock over the reads and
> > the delay?

I wanted to protect the complete hardware operation, from kick-off by
ctrl writing to status change indicating completion, which might
involves delays in between when more than 1 status checks required.