linux-kernel - Re: [PATCH v1 8/9] PCI: PLDA: starfive: Add JH7110 PCIe controller

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Message-ID: <20230802171805.GA62238@bhelgaas>
Date:   Wed, 2 Aug 2023 12:18:05 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kevin Xie <kevin.xie@...rfivetech.com>
Cc:     Minda Chen <minda.chen@...rfivetech.com>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        Conor Dooley <conor@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Emil Renner Berthing <emil.renner.berthing@...onical.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-pci@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Mason Huo <mason.huo@...rfivetech.com>,
        Leyfoon Tan <leyfoon.tan@...rfivetech.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Pali Rohár <pali@...nel.org>,
        Marek Behún <kabel@...nel.org>
Subject: Re: [PATCH v1 8/9] PCI: PLDA: starfive: Add JH7110 PCIe controller

On Tue, Aug 01, 2023 at 03:05:46PM +0800, Kevin Xie wrote:
> On 2023/8/1 7:12, Bjorn Helgaas wrote:
> ...

> > The delay required by sec 6.6.1 is a minimum of 100ms following exit
> > from reset or, for fast links, 100ms after link training completes.
> > 
> > The comment at the call of advk_pcie_wait_for_link() [2] says it is
> > the delay required by sec 6.6.1, but that doesn't seem right to me.
> > 
> > For one thing, I don't think 6.6.1 says anything about "link up" being
> > the end of a delay.  So if we want to do the delay required by 6.6.1,
> > "wait_for_link()" doesn't seem like quite the right name.
> > 
> > For another, all the *_wait_for_link() functions can return success
> > after 0ms, 90ms, 180ms, etc.  They're unlikely to return after 0ms,
> > but 90ms is quite possible.  If we avoided the 0ms return and
> > LINK_WAIT_USLEEP_MIN were 100ms instead of 90ms, that should be enough
> > for slow links, where we need 100ms following "exit from reset."
> > 
> > But it's still not enough for fast links where we need 100ms "after
> > link training completes" because we don't know when training
> > completed.  If training completed 89ms into *_wait_for_link(), we only
> > delay 1ms after that.
> 
> That's the point, we will add a extra 100ms after PERST# de-assert
> in the patch-v3 according to Base Spec r6.0 - 6.6.1:
>         msleep(100);
>         gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> 
> +       /* As the requirement in PCIe base spec r6.0, system must wait a
> +        * minimum of 100 ms following exit from a Conventional Reset
> +        * before sending a Configuration Request to the device.*/
> +       msleep(100);
> +
>         if (starfive_pcie_host_wait_for_link(pcie))
>                 return -EIO;

For fast links (links that support > 5.0 GT/s), the 100ms starts
*after* link training completes.  The above looks OK if starfive only
supports slow links, but then I'm not sure why we would need
starfive_pcie_host_wait_for_link().

Bjorn