linux-kernel - Re: [Patch v4 10/10] PCI: tegra194: add interconnect support in Tegra234

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Date:   Wed, 29 Mar 2023 23:28:40 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
CC:     <treding@...dia.com>, <krzysztof.kozlowski@...aro.org>,
        <dmitry.osipenko@...labora.com>, <viresh.kumar@...aro.org>,
        <rafael@...nel.org>, <jonathanh@...dia.com>, <robh+dt@...nel.org>,
        <lpieralisi@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <mmaddireddy@...dia.com>, <kw@...ux.com>, <bhelgaas@...gle.com>,
        <vidyas@...dia.com>, <sanjayc@...dia.com>, <ksitaraman@...dia.com>,
        <ishah@...dia.com>, <bbasu@...dia.com>,
        Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch v4 10/10] PCI: tegra194: add interconnect support in
 Tegra234



On 29/03/23 22:29, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Wed, Mar 29, 2023 at 02:44:34PM +0530, Sumit Gupta wrote:
>> On 28/03/23 23:23, Bjorn Helgaas wrote:
>>>> +static void tegra_pcie_icc_set(struct tegra_pcie_dw *pcie)
>>>> +{
>>>> +     struct dw_pcie *pci = &pcie->pci;
>>>> +     u32 val, speed, width;
>>>> +
>>>> +     val = dw_pcie_readw_dbi(pci, pcie->pcie_cap_base + PCI_EXP_LNKSTA);
>>>> +
>>>> +     speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, val);
>>>> +     width = FIELD_GET(PCI_EXP_LNKSTA_NLW, val);
>>>> +
>>>> +     val = width * (PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]) / BITS_PER_BYTE);
>>>> +
>>>> +     if (icc_set_bw(pcie->icc_path, MBps_to_icc(val), 0))
>>>> +             dev_err(pcie->dev, "can't set bw[%u]\n", val);
>>>> +
>>>> +     clk_set_rate(pcie->core_clk, pcie_gen_freq[speed - 1]);
>>>
>>> Array bounds violation; PCI_EXP_LNKSTA_CLS is 0x000f, so possible
>>> speed (CLS) values are 0..0xf and "speed - 1" values are -1..0xe.
>>>
>>> pcie_gen_freq[] is of size 4 (valid indices 0..3).
>>>
>>> I see that you're just *moving* this code, but might as well fix it.
>>>
>> Thank you for the review.
>> Will include the below change in the same patch. Please let me know if any
>> issue.
>>
>>   -       clk_set_rate(pcie->core_clk, pcie_gen_freq[speed - 1]);
>>   +       if (speed && (speed <= ARRAY_SIZE(pcie_gen_freq)))
>>   +               clk_set_rate(pcie->core_clk, pcie_gen_freq[speed - 1]);
>>   +       else
>>   +               clk_set_rate(pcie->core_clk, pcie_gen_freq[0]);
> 
> I didn't notice that speed is a u32, so -1 is not a possible value.
> Also, it's used earlier for PCIE_SPEED2MBS_ENC(), so you could do
> something like this:
> 
>    speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, val) - 1;
>    if (speed >= ARRAY_SIZE(pcie_gen_freq))
>      speed = 0;
> 
>    val = width * (PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]) /
>          BITS_PER_BYTE);
>    ...
>    clk_set_rate(pcie->core_clk, pcie_gen_freq[speed]);

I tried this change but PCIE_SPEED2MBS_ENC gives zero when speed value 
is one. The speed value ranges from "1 to 4" and for value "1", 
pcie_link_speed[speed] gives '0xff'.

  const unsigned char pcie_link_speed[] = {
          PCI_SPEED_UNKNOWN,              /* 0 */

The below change works fine. Please share if its OK to add it in patch.

   speed = FIELD_GET(PCI_EXP_LNKSTA_CLS, val);
   if (!speed || speed >= ARRAY_SIZE(pcie_gen_freq))
           speed = 1;

   val = width * (PCIE_SPEED2MBS_ENC(pcie_link_speed[speed]) / 
BITS_PER_BYTE);

   if (icc_set_bw(pcie->icc_path, MBps_to_icc(val), 0))
           dev_err(pcie->dev, "can't set bw[%u]\n", val);

   clk_set_rate(pcie->core_clk, pcie_gen_freq[speed - 1]);


Thank you,
Sumit Gupta