linux-kernel - Re: [PATCH v2] PCI: aardvark: Don't rely on jiffies while holding spinlock

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Date:   Fri, 27 Sep 2019 10:50:00 +0200
From:   Remi Pommarel <repk@...plefau.lt>
To:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: aardvark: Don't rely on jiffies while holding
 spinlock

Hi Thomas,

On Fri, Sep 27, 2019 at 10:34:20AM +0200, Thomas Petazzoni wrote:
> Hello Remi,
> 
> Thanks for the new iteration!
> 
> On Fri, 27 Sep 2019 10:31:42 +0200
> Remi Pommarel <repk@...plefau.lt> wrote:
> 
> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > index fc0fe4d4de49..ee05ccb2b686 100644
> > --- a/drivers/pci/controller/pci-aardvark.c
> > +++ b/drivers/pci/controller/pci-aardvark.c
> > @@ -175,7 +175,8 @@
> >  	(PCIE_CONF_BUS(bus) | PCIE_CONF_DEV(PCI_SLOT(devfn))	| \
> >  	 PCIE_CONF_FUNC(PCI_FUNC(devfn)) | PCIE_CONF_REG(where))
> >  
> > -#define PIO_TIMEOUT_MS			1
> > +#define PIO_RETRY_CNT			10
> > +#define PIO_RETRY_DELAY			2 /* 2 us*/
> 
> So this changes the timeout from 1ms to just 20us, a division by 50
> from the previous timeout value. From my measurements, it could
> sometime take up to 6us from a single PIO read operation to complete,
> which is getting close to the 20us timeout.
> 
> Shouldn't PIO_RETRY_CNT be kept at 500, so that we keep using a 1ms
> timeout ?

Damn. You right of course, sorry about that.

Thanks

-- 
Remi