Re: [PATCH] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

[Stanimir Varbanov]

Hi Niklas,


On 27.05.19 Ð. 20:15 Ñ., Niklas Cassel wrote:
> 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:
> https://source.codeaurora.org/quic/la/kernel/msm-4.14/tree/drivers/pci/host/pci-msm.c?h=LA.UM.7.1.r1-14000-sm8150.0#n1942
>
> and
>
> https://source.codeaurora.org/quic/la/kernel/msm-4.14/tree/drivers/pci/host/pci-msm.c?h=LA.UM.7.1.r1-14000-sm8150.0#n1949
>
> I would rather not remove these since that might affect existing devices.
>
>
> This new sleep matches matches the sleep in:
> https://source.codeaurora.org/quic/la/kernel/msm-4.14/tree/drivers/pci/host/pci-msm.c?h=LA.UM.7.1.r1-14000-sm8150.0#n3926
>
> > 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.

yes, please move the sleep in qcom_ep_reset_deassert()

with that:

Acked-by: Stanimir Varbanov <svarbanov@xxxxxxxxxx>

regards,
Stan