Re: [PATCH v6 2/2] PCI: iproc: add device shutdown for PCI RC

[Oza Oza]

On Sun, Aug 20, 2017 at 2:34 AM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
> On Fri, Aug 04, 2017 at 09:18:16PM +0530, Oza Pawandeep wrote:
>> PERST must be asserted around ~500ms before the reboot is applied.
>>
>> During soft reset (e.g., "reboot" from Linux) on some iproc based SOCs
>> LCPLL clock and PERST both goes off simultaneously.
>> This will cause certain Endpoints Intel NVMe not get detected, upon
>> next boot sequence.
>>
>> This is specifically happening with Intel P3700 400GB series.
>> Endpoint is expecting the clock for some amount of time after PERST is
>> asserted, which is not happening in Stingray (iproc based SOC).
>> This causes NVMe to behave in undefined way.
>>
>> On the contrary, Intel x86 boards will have ref clock running, so we
>> do not see this behavior there.
>>
>> Besides, PCI spec does not stipulate about such timings.
>> In-fact it does not tell us, whether PCIe device should consider
>> refclk to be available or not to be.
>>
>> It is completely up to vendor to design their EP the way they want
>> with respect to ref clock availability.
>
> I am unconvinced.  Designing an endpoint that relies on ref clock
> timing not guaranteed by the spec does not sound like a way to build
> reliable hardware.
>
> The PCIe Card Electromechanical spec, r2.0, sec 2.2.3 says the clock
> goes inactive after PERST# goes active, but doesn't specify how long.
> In the absence of a spec requirement, I don't see a reason to assume
> other systems preserve the ref clock after PERST#, so if the Intel
> device requires clocks for 500ms after PERST#, we should see problems
> on other systems.

The reason you do not see and most likely you will not see on any
other system is
because, the ref clock is supplied by on board oscillator.
when PERST# is asserted, the ref clock is still available.

but in our case, we do not have on-board clock generator, rather we
rely on the clock
coming from SOC, so if SOC reset is issued, both PERST# and the ref
clock goes off simultaneously.

please also refer to the link below which stipulate on clk being
active after PERST# being asserted.
http://www.eetimes.com/document.asp?doc_id=1279299  [Figure 2:
Power-down waveforms]

however I am not saying that, this article has more to claim than PCIe spec.
but, I think the PCIe Card Electromechanical spec leaves the margin
for card manufactures to design the card based on the assumption
that ref clock could be available after PERST#  is asserted.

most of the cards do not assume that, but at the least we have seen that,
once particular card which behaves as per the link which I have just
pasted above.

>
> Sec 2.2 says that on power up, the power rails must be stable at least
> T(PVPERL) (100ms) and reference clocks must be stable at least
> T(PERST-CLK) (100us) before PERST# is deasserted.  I think it's more
> likely the problem is here.
>
> The current iproc_pcie_reset() looks like it sleeps 100ms *after* it
> deasserts PERST#.  Should that be *before* deasserting PERST#?
>

T(PERST-CLK) (100us) before PERST# is deasserted.
which we are already waiting for 250us

T(PVPERL) (100ms), the power rail is stable much before linux comes up.
so I still think we are meeting power up requirements.

>> 500ms is just based on the observation and taken as safe margin.
>> This patch adds platform shutdown where it should be
>> called in device_shutdown while reboot command is issued.
>> So in sequence first Endpoint Shutdown (e.g. nvme_shutdown)
>> followed by RC shutdown, which issues safe PERST assertion.
>>
>> Signed-off-by: Oza Pawandeep <oza.oza@xxxxxxxxxxxx>
>> Reviewed-by: Ray Jui <ray.jui@xxxxxxxxxxxx>
>> Reviewed-by: Scott Branden <scott.branden@xxxxxxxxxxxx>
>>
>> diff --git a/drivers/pci/host/pcie-iproc-platform.c b/drivers/pci/host/pcie-iproc-platform.c
>> index 90d2bdd..9512960 100644
>> --- a/drivers/pci/host/pcie-iproc-platform.c
>> +++ b/drivers/pci/host/pcie-iproc-platform.c
>> @@ -131,6 +131,13 @@ static int iproc_pcie_pltfm_remove(struct platform_device *pdev)
>>       return iproc_pcie_remove(pcie);
>>  }
>>
>> +static void iproc_pcie_pltfm_shutdown(struct platform_device *pdev)
>> +{
>> +     struct iproc_pcie *pcie = platform_get_drvdata(pdev);
>> +
>> +     iproc_pcie_shutdown(pcie);
>> +}
>> +
>>  static struct platform_driver iproc_pcie_pltfm_driver = {
>>       .driver = {
>>               .name = "iproc-pcie",
>> @@ -138,6 +145,7 @@ static int iproc_pcie_pltfm_remove(struct platform_device *pdev)
>>       },
>>       .probe = iproc_pcie_pltfm_probe,
>>       .remove = iproc_pcie_pltfm_remove,
>> +     .shutdown = iproc_pcie_pltfm_shutdown,
>>  };
>>  module_platform_driver(iproc_pcie_pltfm_driver);
>>
>> diff --git a/drivers/pci/host/pcie-iproc.c b/drivers/pci/host/pcie-iproc.c
>> index 583cee0..ee40651 100644
>> --- a/drivers/pci/host/pcie-iproc.c
>> +++ b/drivers/pci/host/pcie-iproc.c
>> @@ -627,7 +627,7 @@ static int iproc_pcie_config_write32(struct pci_bus *bus, unsigned int devfn,
>>       .write = iproc_pcie_config_write32,
>>  };
>>
>> -static void iproc_pcie_reset(struct iproc_pcie *pcie)
>> +static void iproc_pcie_perst_ctrl(struct iproc_pcie *pcie, bool assert)
>>  {
>>       u32 val;
>>
>> @@ -639,20 +639,28 @@ static void iproc_pcie_reset(struct iproc_pcie *pcie)
>>       if (pcie->ep_is_internal)
>>               return;
>>
>> -     /*
>> -      * Select perst_b signal as reset source. Put the device into reset,
>> -      * and then bring it out of reset
>> -      */
>> -     val = iproc_pcie_read_reg(pcie, IPROC_PCIE_CLK_CTRL);
>> -     val &= ~EP_PERST_SOURCE_SELECT & ~EP_MODE_SURVIVE_PERST &
>> -             ~RC_PCIE_RST_OUTPUT;
>> -     iproc_pcie_write_reg(pcie, IPROC_PCIE_CLK_CTRL, val);
>> -     udelay(250);
>> -
>> -     val |= RC_PCIE_RST_OUTPUT;
>> -     iproc_pcie_write_reg(pcie, IPROC_PCIE_CLK_CTRL, val);
>> -     msleep(100);
>> +     if (assert) {
>> +             val = iproc_pcie_read_reg(pcie, IPROC_PCIE_CLK_CTRL);
>> +             val &= ~EP_PERST_SOURCE_SELECT & ~EP_MODE_SURVIVE_PERST &
>> +                     ~RC_PCIE_RST_OUTPUT;
>> +             iproc_pcie_write_reg(pcie, IPROC_PCIE_CLK_CTRL, val);
>> +             udelay(250);
>> +     } else {
>> +             val = iproc_pcie_read_reg(pcie, IPROC_PCIE_CLK_CTRL);
>> +             val |= RC_PCIE_RST_OUTPUT;
>> +             iproc_pcie_write_reg(pcie, IPROC_PCIE_CLK_CTRL, val);
>> +             msleep(100);
>> +     }
>> +}