Re: [PATCH v2] PCI: qcom: Ensure that PERST is asserted for at least 100 ms

Lorenzo Pieralisi
2019-05-30T15:55:03Z

On Wed, May 29, 2019 at 11:43:52AM +0200, 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.
>
> Fixes: 82a823833f4e ("PCI: qcom: Add Qualcomm PCIe controller driver")
> Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
> Acked-by: Stanimir Varbanov <svarbanov@mm-sol.com>
> Cc: stable@vger.kernel.org # 4.5+
> ---
> Changes since v1:
> Move the sleep into qcom_ep_reset_deassert()
>
> drivers/pci/controller/dwc/pcie-qcom.c | 2 ++
> 1 file changed, 2 insertions(+)

Applied to pci/qcom for v5.3, thanks.

Lorenzo

> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 0ed235d560e3..5d1713069d14 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -178,6 +178,8 @@ static void qcom_ep_reset_assert(struct qcom_pcie *pcie)
>
> static void qcom_ep_reset_deassert(struct qcom_pcie *pcie)
> {
> + /* Ensure that PERST has been asserted for at least 100 ms */
> + msleep(100);
> gpiod_set_value_cansleep(pcie->reset, 0);
> usleep_range(PERST_DELAY_US, PERST_DELAY_US + 500);
> }
> --
> 2.21.0
>