linux-kernel - Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before training link

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Message-ID: <20191014153919.GB2928@e121166-lin.cambridge.arm.com>
Date:   Mon, 14 Oct 2019 16:39:19 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Remi Pommarel <repk@...plefau.lt>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Ellie Reeves <ellierevves@...il.com>,
        linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: aardvark: Wait for endpoint to be ready before
 training link

On Tue, Aug 06, 2019 at 08:49:46PM +0200, Remi Pommarel wrote:
> On Wed, May 22, 2019 at 11:33:50PM +0200, Remi Pommarel wrote:
> > When configuring pcie reset pin from gpio (e.g. initially set by
> > u-boot) to pcie function this pin goes low for a brief moment
> > asserting the PERST# signal. Thus connected device enters fundamental
> > reset process and link configuration can only begin after a minimal
> > 100ms delay (see [1]).
> > 
> > Because the pin configuration comes from the "default" pinctrl it is
> > implicitly configured before the probe callback is called:
> > 
> > driver_probe_device()
> >   really_probe()
> >     ...
> >     pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
> >                            function and PERST# is asserted */
> >     ...
> >     drv->probe()
> > 
> > [1] "PCI Express Base Specification", REV. 4.0
> >     PCI Express, February 19 2014, 6.6.1 Conventional Reset
> > 
> > Signed-off-by: Remi Pommarel <repk@...plefau.lt>
> > ---
> > Changes since v1:
> >   - Add a comment about pinctrl implicit pin configuration
> >   - Use more legible msleep
> >   - Use PCI_PM_D3COLD_WAIT macro
> > 
> > Please note that I will unlikely be able to answer any comments from May
> > 24th to June 10th.
> > ---
> >  drivers/pci/controller/pci-aardvark.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > index 134e0306ff00..d998c2b9cd04 100644
> > --- a/drivers/pci/controller/pci-aardvark.c
> > +++ b/drivers/pci/controller/pci-aardvark.c
> > @@ -324,6 +324,14 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
> >  	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
> >  	advk_writel(pcie, reg, PIO_CTRL);
> >  
> > +	/*
> > +	 * PERST# signal could have been asserted by pinctrl subsystem before
> > +	 * probe() callback has been called, making the endpoint going into
> > +	 * fundamental reset. As required by PCI Express spec a delay for at
> > +	 * least 100ms after such a reset before link training is needed.
> > +	 */
> > +	msleep(PCI_PM_D3COLD_WAIT);
> > +
> >  	/* Start link training */
> >  	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
> >  	reg |= PCIE_CORE_LINK_TRAINING;
> > -- 
> > 2.20.1
> 
> Gentle ping.

Thomas, sorry for the delay, unless you object I would merge this
patch, I need your ACK to proceed though.

Thanks,
Lorenzo