Re: [PATCH] pci: aardvark: Wait for endpoint to be ready before training link

Remi Pommarel
2019-04-23T22:20:23Z

Hi,

On Tue, Apr 23, 2019 at 05:32:15PM +0100, Lorenzo Pieralisi wrote:
> On Wed, Mar 13, 2019 at 10:37:52PM +0100, 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]).
> >
> > This makes sure that link is configured after at least 100ms from
> > beginning of probe() callback (shortly after the reset pin function
> > configuration switch through pinctrl subsytem).
> >
> > [1] "PCI Express Base Specification", REV. 2.1
> > PCI Express, March 4 2009, 6.6.1 Conventional Reset
> >
> > Signed-off-by: Remi Pommarel <repk@triplefau.lt>
> > ---
> > drivers/pci/controller/pci-aardvark.c | 17 ++++++++++++++---
> > 1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> > index a30ae7cf8e7e..70a1023d0ef1 100644
> > --- a/drivers/pci/controller/pci-aardvark.c
> > +++ b/drivers/pci/controller/pci-aardvark.c
> > @@ -177,6 +177,9 @@
> >
> > #define PIO_TIMEOUT_MS 1
> >
> > +/* Endpoint can take up to 100ms to be ready after a reset */
> > +#define ENDPOINT_RST_MS 100
> > +
> > #define LINK_WAIT_MAX_RETRIES 10
> > #define LINK_WAIT_USLEEP_MIN 90000
> > #define LINK_WAIT_USLEEP_MAX 100000
> > @@ -242,8 +245,10 @@ static int advk_pcie_wait_for_link(struct advk_pcie *pcie)
> > return -ETIMEDOUT;
> > }
> >
> > -static void advk_pcie_setup_hw(struct advk_pcie *pcie)
> > +static void
> > +advk_pcie_setup_hw(struct advk_pcie *pcie, unsigned long ep_rdy_time)
>
> Nit: I prefer the prototype to be in one line, I wrap it for you.
>
> I am wondering why you need to pass in ep_rdy_time parameter when you
> can easily compute it in the function itself.
>

The only reason for that is because the sooner I get the jiffies the
lower the delay has to be. I was trying to reduce the impact of this
delay to a minimum, but maybe the improvement is not worth it.

--
Remi