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

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Message-ID: <20230329165957.GA3066317@bhelgaas>
Date:   Wed, 29 Mar 2023 11:59:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sumit Gupta <sumitg@...dia.com>
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
Subject: Re: [Patch v4 10/10] PCI: tegra194: add interconnect support in
 Tegra234

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]);