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

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Message-ID: <26834aba-4d45-6da4-0548-1fb61e684b59@nvidia.com>
Date:   Mon, 8 Mar 2021 16:12:55 +0530
From:   Om Prakash Singh <omp@...dia.com>
To:     Vidya Sagar <vidyas@...dia.com>, Bjorn Helgaas <helgaas@...nel.org>
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 11:43 PM, Vidya Sagar wrote:
> 
> 
> 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.
>
I'll take care of this in next patch version
 
>>
>>> 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;" ?
>
This cannot be clubbed as PTM root capability needs to disable first before disabling responded capability 
 
>>> +             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
>>>