Re: [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms
From: Niklas Cassel
Date: Mon May 27 2019 - 13:18:44 EST
On Fri, May 24, 2019 at 02:43:00PM +0200, Marc Gonzalez wrote:
> On 23/05/2019 21:44, Niklas Cassel wrote:
> > Currently, there is only a 1 ms sleep after asserting PERST.
> > Reading the datasheets for different endpoints, some require PERST to be
> > asserted for 10 ms in order for the endpoint to perform a reset, others
> > require it to be asserted for 50 ms.
> > Several SoCs using this driver uses PCIe Mini Card, where we don't know
> > what endpoint will be plugged in.
> > The PCI Express Card Electromechanical Specification specifies:
> > "On power up, the deassertion of PERST# is delayed 100 ms (TPVPERL) from
> > the power rails achieving specified operating limits."
> > Add a sleep of 100 ms before deasserting PERST, in order to ensure that
> > we are compliant with the spec.
> > Signed-off-by: Niklas Cassel <niklas.cassel@xxxxxxxxxx>
> > ---
> > drivers/pci/controller/dwc/pcie-qcom.c | 2 ++
> > 1 file changed, 2 insertions(+)
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > index 0ed235d560e3..cae24376237c 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -1110,6 +1110,8 @@ static int qcom_pcie_host_init(struct pcie_port *pp)
> > if (IS_ENABLED(CONFIG_PCI_MSI))
> > dw_pcie_msi_init(pp);
> > + /* Ensure that PERST has been asserted for at least 100 ms */
> > + msleep(100);
> > qcom_ep_reset_deassert(pcie);
> > ret = qcom_pcie_establish_link(pcie);
> Currently, qcom_ep_reset_assert() and qcom_ep_reset_deassert() both include
> a call to usleep_range() of 1.0 to 1.5 ms
> Can we git rid of both if we sleep 100 ms before qcom_ep_reset_deassert?
These two sleeps after asserting/deasserting reset in qcom_ep_reset_assert()/
qcom_ep_reset_deassert() matches the sleeps in:
I would rather not remove these since that might affect existing devices.
This new sleep matches matches the sleep in:
> Should the msleep() call be included in one of the two wrappers?
This new sleep could be moved into qcom_ep_reset_deassert(),
added before the gpiod_set_value_cansleep(pcie->reset, 0) call,
if Stanimir prefers it to be placed there instead.