Re: [PATCH] PCI: qcom-ep: Move controller cleanups to qcom_pcie_perst_deassert()

[Manivannan Sadhasivam]

On Mon, Jul 29, 2024 at 05:58:31PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 7/29/2024 5:52 PM, Manivannan Sadhasivam wrote:
> > Currently, the endpoint cleanup function dw_pcie_ep_cleanup() and EPF
> > deinit notify function pci_epc_deinit_notify() are called during the
> > execution of qcom_pcie_perst_assert() i.e., when the host has asserted
> > PERST#. But quickly after this step, refclk will also be disabled by the
> > host.
> > 
> > All of the Qcom endpoint SoCs supported as of now depend on the refclk from
> > the host for keeping the controller operational. Due to this limitation,
> > any access to the hardware registers in the absence of refclk will result
> > in a whole endpoint crash. Unfortunately, most of the controller cleanups
> > require accessing the hardware registers (like eDMA cleanup performed in
> > dw_pcie_ep_cleanup(), powering down MHI EPF etc...). So these cleanup
> > functions are currently causing the crash in the endpoint SoC once host
> > asserts PERST#.
> > 
> > One way to address this issue is by generating the refclk in the endpoint
> > itself and not depending on the host. But that is not always possible as
> > some of the endpoint designs do require the endpoint to consume refclk from
> > the host (as I was told by the Qcom engineers).
> > 
> > So let's fix this crash by moving the controller cleanups to the start of
> > the qcom_pcie_perst_deassert() function. qcom_pcie_perst_deassert() is
> > called whenever the host has deasserted PERST# and it is guaranteed that
> > the refclk would be active at this point. So at the start of this function,
> > the controller cleanup can be performed. Once finished, rest of the code
> > execution for PERST# deassert can continue as usual.
> > 
> How about doing the cleanup as part of pme turnoff message.
> As host waits for L23 ready from the device side. we can use that time
> to cleanup the host before sending L23 ready.
> 

Yes, but that's only applicable if the host properly powers down the device. But
it won't work in the case of host crash or host abrupt poweroff.

- Mani

> - Krishna Chaitanya.
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxx>
> > ---
> >   drivers/pci/controller/dwc/pcie-qcom-ep.c | 12 ++++++++++--
> >   1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > index 2319ff2ae9f6..e024b4dcd76d 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > @@ -186,6 +186,8 @@ struct qcom_pcie_ep_cfg {
> >    * @link_status: PCIe Link status
> >    * @global_irq: Qualcomm PCIe specific Global IRQ
> >    * @perst_irq: PERST# IRQ
> > + * @cleanup_pending: Cleanup is pending for the controller (because refclk is
> > + *                   needed for cleanup)
> >    */
> >   struct qcom_pcie_ep {
> >   	struct dw_pcie pci;
> > @@ -214,6 +216,7 @@ struct qcom_pcie_ep {
> >   	enum qcom_pcie_ep_link_status link_status;
> >   	int global_irq;
> >   	int perst_irq;
> > +	bool cleanup_pending;
> >   };
> >   static int qcom_pcie_ep_core_reset(struct qcom_pcie_ep *pcie_ep)
> > @@ -389,6 +392,12 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
> >   		return ret;
> >   	}
> > +	if (pcie_ep->cleanup_pending) {
> > +		pci_epc_deinit_notify(pci->ep.epc);
> > +		dw_pcie_ep_cleanup(&pci->ep);
> > +		pcie_ep->cleanup_pending = false;
> > +	}
> > +
> >   	/* Assert WAKE# to RC to indicate device is ready */
> >   	gpiod_set_value_cansleep(pcie_ep->wake, 1);
> >   	usleep_range(WAKE_DELAY_US, WAKE_DELAY_US + 500);
> > @@ -522,10 +531,9 @@ static void qcom_pcie_perst_assert(struct dw_pcie *pci)
> >   {
> >   	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > -	pci_epc_deinit_notify(pci->ep.epc);
> > -	dw_pcie_ep_cleanup(&pci->ep);
> >   	qcom_pcie_disable_resources(pcie_ep);
> >   	pcie_ep->link_status = QCOM_PCIE_EP_LINK_DISABLED;
> > +	pcie_ep->cleanup_pending = true;
> >   }
> >   /* Common DWC controller ops */

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