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

[Stanimir Varbanov <svarbanov@mm-sol.com>]

Hi Niklas,


On 27.05.19 г. 20:15 ч., 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@linaro.org>
>>> ---
>>>   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@mm-sol.com>

regards,
Stan