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Message-ID: <92c4854d-033e-c7b5-ca92-cf44a1a8c0cc@oss.qualcomm.com>
Date: Fri, 28 Mar 2025 11:04:11 +0530
From: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley
<conor+dt@...nel.org>,
Bjorn Helgaas <bhelgaas@...gle.com>, Jingoo Han <jingoohan1@...il.com>,
Lorenzo Pieralisi
<lpieralisi@...nel.org>,
Krzysztof WilczyĆski
<kw@...ux.com>,
linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
quic_mrana@...cinc.com, quic_vbadigan@...cinc.com
Subject: Re: [PATCH v8 4/4] PCI: dwc: Add support for configuring lane
equalization presets
On 3/28/2025 10:23 AM, Manivannan Sadhasivam wrote:
> On Sun, Mar 16, 2025 at 09:39:04AM +0530, Krishna Chaitanya Chundru wrote:
>> PCIe equalization presets are predefined settings used to optimize
>> signal integrity by compensating for signal loss and distortion in
>> high-speed data transmission.
>>
>> Based upon the number of lanes and the data rate supported, write
>> the preset data read from the device tree in to the lane equalization
>> control registers.
>>
>> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
>> ---
>> drivers/pci/controller/dwc/pcie-designware-host.c | 60 +++++++++++++++++++++++
>> drivers/pci/controller/dwc/pcie-designware.h | 3 ++
>> include/uapi/linux/pci_regs.h | 3 ++
>> 3 files changed, 66 insertions(+)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
>> index dd56cc02f4ef..7c6e6a74383b 100644
>> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
>> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
>> @@ -507,6 +507,10 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>> if (pci->num_lanes < 1)
>> pci->num_lanes = dw_pcie_link_get_max_link_width(pci);
>>
>> + ret = of_pci_get_equalization_presets(dev, &pp->presets, pci->num_lanes);
>> + if (ret)
>> + goto err_free_msi;
>> +
>> /*
>> * Allocate the resource for MSG TLP before programming the iATU
>> * outbound window in dw_pcie_setup_rc(). Since the allocation depends
>> @@ -808,6 +812,61 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
>> return 0;
>> }
>>
>> +static void dw_pcie_program_presets(struct dw_pcie_rp *pp, enum pci_bus_speed speed)
>> +{
>> + struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>> + u8 lane_eq_offset, lane_reg_size, cap_id;
>> + u8 *presets;
>> + u32 cap;
>> + int i;
>> +
>> + if (speed == PCIE_SPEED_8_0GT) {
>> + presets = (u8 *)pp->presets.eq_presets_8gts;
>> + lane_eq_offset = PCI_SECPCI_LE_CTRL;
>> + cap_id = PCI_EXT_CAP_ID_SECPCI;
>> + /* For data rate of 8 GT/S each lane equalization control is 16bits wide*/
>> + lane_reg_size = 0x2;
>> + } else if (speed == PCIE_SPEED_16_0GT) {
>> + presets = pp->presets.eq_presets_Ngts[EQ_PRESET_TYPE_16GTS - 1];
>> + lane_eq_offset = PCI_PL_16GT_LE_CTRL;
>> + cap_id = PCI_EXT_CAP_ID_PL_16GT;
>> + lane_reg_size = 0x1;
>> + } else {
>
> Can you add conditions for other data rates also? Like 32, 64 GT/s. If
> controller supports them and if the presets property is defined in DT, then you
> should apply the preset values.
>
> If the presets property is not present in DT, then below 'PCI_EQ_RESV' will
> safely return.
>
I am fine to add it, but there is no GEN5 or GEN6 controller support
added in dwc, isn't it best to add when that support is added and
tested.
- Krishna Chaitanya.
>> + return;
>> + }
>> +
>> + if (presets[0] == PCI_EQ_RESV)
>> + return;
>> +
>> + cap = dw_pcie_find_ext_capability(pci, cap_id);
>> + if (!cap)
>> + return;
>> +
>> + /*
>> + * Write preset values to the registers byte-by-byte for the given
>> + * number of lanes and register size.
>> + */
>> + for (i = 0; i < pci->num_lanes * lane_reg_size; i++)
>> + dw_pcie_writeb_dbi(pci, cap + lane_eq_offset + i, presets[i]);
>> +}
>> +
>> +static void dw_pcie_config_presets(struct dw_pcie_rp *pp)
>> +{
>> + struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>> + enum pci_bus_speed speed = pcie_link_speed[pci->max_link_speed];
>> +
>> + /*
>> + * Lane equalization needs to be perfomed for all data rates
>> + * the controller supports and for all supported lanes.
>> + */
>> +
>> + if (speed >= PCIE_SPEED_8_0GT)
>> + dw_pcie_program_presets(pp, PCIE_SPEED_8_0GT);
>> +
>> + if (speed >= PCIE_SPEED_16_0GT)
>> + dw_pcie_program_presets(pp, PCIE_SPEED_16_0GT);
>
> Add other data rates also.
>
> - Mani
>
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