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

[Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>]

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@oss.qualcomm.com>
>> Link[1]: https://lore.kernel.org/all/20260205093346.667898-1-krishna.chundru@oss.qualcomm.com/
>> ---
>>   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.

- Krishna Chaitanya.
>
> - Mani
>