linux-kernel - Re: [PATCH] PCI: tegra: Disable PTM capabilities for EP mode

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Date:   Fri, 5 Mar 2021 23:43:05 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Om Prakash Singh <omp@...dia.com>
CC:     <jingoohan1@...il.com>, <gustavo.pimentel@...opsys.com>,
        <lorenzo.pieralisi@....com>, <amurray@...goodpenguin.co.uk>,
        <bhelgaas@...gle.com>, <kishon@...com>, <thierry.reding@...il.com>,
        <Jisheng.Zhang@...aptics.com>, <jonathanh@...dia.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kthota@...dia.com>, <mmaddireddy@...dia.com>,
        <oop.singh@...il.com>
Subject: Re: [PATCH] PCI: tegra: Disable PTM capabilities for EP mode



On 3/5/2021 5:49 PM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Fri, Mar 05, 2021 at 01:42:34PM +0530, Om Prakash Singh wrote:
>> PCIe EP compliance expect PTM capabilities (ROOT_CAPABLE, RES_CAPABLE,
>> CLK_GRAN) to be disabled.
> 
> I guess this is just enforcing the PCIe spec requirements that only
> Root Ports, RCRBs, and Switches are allowed to set the PTM Responder
> Capable bit, and that the Local Clock Granularity is RsvdP if PTM Root
> Capable is zero?  (PCIe r5.0, sec 7.9.16.2)
> 
> Should this be done more generally somewhere in the dwc code as
> opposed to in the tegra code?
Agree.

> 
>> Signed-off-by: Om Prakash Singh <omp@...dia.com>
>> ---
>>   drivers/pci/controller/dwc/pcie-tegra194.c | 17 ++++++++++++++++-
>>   include/uapi/linux/pci_regs.h              |  1 +
>>   2 files changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c b/drivers/pci/controller/dwc/pcie-tegra194.c
>> index 6fa216e..a588312 100644
>> --- a/drivers/pci/controller/dwc/pcie-tegra194.c
>> +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
>> @@ -1639,7 +1639,7 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
>>        struct dw_pcie *pci = &pcie->pci;
>>        struct dw_pcie_ep *ep = &pci->ep;
>>        struct device *dev = pcie->dev;
>> -     u32 val;
>> +     u32 val, ptm_cap_base = 0;
> 
> Unnecessary init.
> 
>>        int ret;
>>
>>        if (pcie->ep_state == EP_STATE_ENABLED)
>> @@ -1760,6 +1760,21 @@ static void pex_ep_event_pex_rst_deassert(struct tegra_pcie_dw *pcie)
>>                                                      PCI_CAP_ID_EXP);
>>        clk_set_rate(pcie->core_clk, GEN4_CORE_CLK_FREQ);
>>
>> +     /* Disable PTM root and responder capability */
>> +     ptm_cap_base = dw_pcie_find_ext_capability(&pcie->pci,
>> +                                                PCI_EXT_CAP_ID_PTM);
>> +     if (ptm_cap_base) {
>> +             dw_pcie_dbi_ro_wr_en(pci);
>> +             val = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
>> +             val &= ~PCI_PTM_CAP_ROOT;
>> +             dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, val);
>> +
>> +             val = dw_pcie_readl_dbi(pci, ptm_cap_base + PCI_PTM_CAP);
>> +             val &= ~(PCI_PTM_CAP_RES | PCI_PTM_GRANULARITY_MASK);
Why can't this be clubbed with "val &= ~PCI_PTM_CAP_ROOT;" ?

>> +             dw_pcie_writel_dbi(pci, ptm_cap_base + PCI_PTM_CAP, val);
>> +             dw_pcie_dbi_ro_wr_dis(pci);
>> +     }
>> +
>>        val = (ep->msi_mem_phys & MSIX_ADDR_MATCH_LOW_OFF_MASK);
>>        val |= MSIX_ADDR_MATCH_LOW_OFF_EN;
>>        dw_pcie_writel_dbi(pci, MSIX_ADDR_MATCH_LOW_OFF, val);
>> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
>> index e709ae8..9dd6f8d 100644
>> --- a/include/uapi/linux/pci_regs.h
>> +++ b/include/uapi/linux/pci_regs.h
>> @@ -1050,6 +1050,7 @@
>>   /* Precision Time Measurement */
>>   #define PCI_PTM_CAP                  0x04        /* PTM Capability */
>>   #define  PCI_PTM_CAP_REQ             0x00000001  /* Requester capable */
>> +#define  PCI_PTM_CAP_RES             0x00000002  /* Responder capable */
>>   #define  PCI_PTM_CAP_ROOT            0x00000004  /* Root capable */
>>   #define  PCI_PTM_GRANULARITY_MASK    0x0000FF00  /* Clock granularity */
>>   #define PCI_PTM_CTRL                 0x08        /* PTM Control */
>> --
>> 2.7.4
>>