Re: [PATCH v3 3/3] PCI: qcom: Program T_POWER_ON

[Manivannan Sadhasivam]

On Mon, Mar 16, 2026 at 10:35:50AM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 3/16/2026 10:23 AM, Manivannan Sadhasivam wrote:
> > On Wed, Mar 11, 2026 at 06:10:40PM +0530, Krishna Chaitanya Chundru wrote:
> > > Some platforms have incorrect T_POWER_ON value programmed in hardware.
> > > Generally these will be corrected by bootloaders, but not all targets
> > > support bootloaders to program correct values due to that
> > > LTR_L1.2_THRESHOLD value calculated by aspm driver can be wrong, which
> > > can result in improper L1.2 exit behavior and if AER happens to be
> > > supported and enabled, the error may be *reported* via AER.
> > > 
> > > Parse "t-power-on-us" property from each root port node and program them
> > > as part of host initialization using dw_pcie_program_t_power_on() before
> > > link training.
> > > 
> > > This property in added to the dtschema here[1].
> > > 
> > > Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@xxxxxxxxxxxxxxxx>
> > > Link[1]: https://lore.kernel.org/all/20260205093346.667898-1-krishna.chundru@xxxxxxxxxxxxxxxx/
> > > ---
> > >   drivers/pci/controller/dwc/pcie-qcom.c | 13 +++++++++++++
> > >   1 file changed, 13 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > index 67a16af69ddc75fca1b123e70715e692a91a9135..63d5628e988d3c07f42099c0d86e6b80fd54ce32 100644
> > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > @@ -269,6 +269,7 @@ struct qcom_pcie_perst {
> > >   struct qcom_pcie_port {
> > >   	struct list_head list;
> > >   	struct phy *phy;
> > > +	u32 l1ss_t_power_on;
> > >   	struct list_head perst;
> > >   };
> > > @@ -1283,6 +1284,14 @@ static int qcom_pcie_phy_power_on(struct qcom_pcie *pcie)
> > >   	return 0;
> > >   }
> > > +static void qcom_pcie_configure_ports(struct qcom_pcie *pcie)
> > > +{
> > > +	struct qcom_pcie_port *port;
> > > +
> > > +	list_for_each_entry(port, &pcie->ports, list)
> > > +		dw_pcie_program_t_power_on(pcie->pci, port->l1ss_t_power_on);
> > > +}
> > > +
> > >   static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> > >   {
> > >   	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> > > @@ -1317,6 +1326,8 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> > >   	dw_pcie_remove_capability(pcie->pci, PCI_CAP_ID_MSIX);
> > >   	dw_pcie_remove_ext_capability(pcie->pci, PCI_EXT_CAP_ID_DPC);
> > > +	qcom_pcie_configure_ports(pcie);
> > > +
> > >   	qcom_pcie_perst_deassert(pcie);
> > >   	if (pcie->cfg->ops->config_sid) {
> > > @@ -1759,6 +1770,8 @@ static int qcom_pcie_parse_port(struct qcom_pcie *pcie, struct device_node *node
> > >   	if (ret)
> > >   		return ret;
> > > +	of_property_read_u32(node, "t-power-on-us", &port->l1ss_t_power_on);
> > > +
> > Since this is going to be common for all controller drivers, it'd be good to
> > move this inside the dwc API.
> As this per root port, we can summit changes to merge first so that we can
> move this to
> dwc.
> 

Fair. Atleast add a TODO here.

- Mani

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