linux-kernel - Re: [PATCH 1/2] PCI: dra7xx: Fix link removal on probe error

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Date:   Fri, 13 May 2022 20:46:57 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Luca Ceresoli <luca@...aceresoli.net>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>, PCI <linux-pci@...r.kernel.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        linux-omap <linux-omap@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH 1/2] PCI: dra7xx: Fix link removal on probe error

On Thu, May 12, 2022 at 7:07 AM Luca Ceresoli <luca@...aceresoli.net> wrote:
>
> Hi Lorenzo,
>
> On 11/05/22 18:41, Lorenzo Pieralisi wrote:
> > On Sat, Jan 15, 2022 at 10:02:00AM -0600, Rob Herring wrote:
> >> +Saravana
> >>
> >> On Tue, Jan 11, 2022 at 4:35 AM Luca Ceresoli <luca@...aceresoli.net> wrote:
> >>>
> >>> Hi Rob,
> >>>
> >>> On 16/12/21 10:08, Luca Ceresoli wrote:
> >>>> Hi Rob,
> >>>>
> >>>> thanks for the quick feedback!
> >>>>
> >>>> On 14/12/21 23:42, Rob Herring wrote:
> >>>>> On Tue, Dec 14, 2021 at 4:15 PM Luca Ceresoli <luca@...aceresoli.net> wrote:
> >>>>>>
> >>>>>> If a devm_phy_get() calls fails with phy_count==N (N > 0), then N links
> >>>>>> have already been added by device_link_add() and won't be deleted by
> >>>>>> device_link_del() because the code calls 'return' and not 'goto err_link'.
> >>>>>>
> >>>>>> Fix in a very simple way by doing all the devm_phy_get() calls before all
> >>>>>> the device_link_add() calls.
> >>>>>>
> >>>>>> Fixes: 7a4db656a635 ("PCI: dra7xx: Create functional dependency between PCIe and PHY")
> >>>>>> Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
> >>>>>> ---
> >>>>>>  drivers/pci/controller/dwc/pci-dra7xx.c | 2 ++
> >>>>>>  1 file changed, 2 insertions(+)
> >>>>>>
> >>>>>> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
> >>>>>> index f7f1490e7beb..2ccc53869e13 100644
> >>>>>> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
> >>>>>> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
> >>>>>> @@ -757,7 +757,9 @@ static int dra7xx_pcie_probe(struct platform_device *pdev)
> >>>>>>                 phy[i] = devm_phy_get(dev, name);
> >>>>>>                 if (IS_ERR(phy[i]))
> >>>>>>                         return PTR_ERR(phy[i]);
> >>>>>> +       }
> >>>>>>
> >>>>>> +       for (i = 0; i < phy_count; i++) {
> >>>>>>                 link[i] = device_link_add(dev, &phy[i]->dev, DL_FLAG_STATELESS);
> >>>>>
> >>>>> I think this should happen automatically now with fw_devlink being
> >>>>> enabled by default. Can you try?
> >>>>
> >>>> Do you mean removal should be done automatically? I think they are not
> >>>> due to the DL_FLAG_STATELESS flag.
> >>>
> >>> I would love to have feedback because, as said, I think my patch is
> >>> correct, but if I'm wrong (which might well be) I have to drop patch 1
> >>> and rewrite patch 2 in a slightly more complex form.
> >>
> >> I mean that why do you need explicit dependency tracking here when
> >> dependencies on a PHY should happen automatically now. IOW, what is
> >> special about this driver and dependency?
> >
> > Any update on this patch ? I think patch 2 can be merged, please
> > let me know if this one can be dropped.
>
> Thanks for the feedback! You would say yes, you can merge patch 2,
> except it probably does not even apply as it is written in a way that is
> based on the changes in patch 1.
>
> I could rewrite patch 2 to not depend on patch 1 of course, but it
> wouldn't make code simpler, perhaps more complex. And moreover the
> hardware that I used to have access to has phy_count==1 so I could never
> test the failing case, and sadly now I have no access to that hardware.

Hi Luca,

The fw_devlink code to create device links from consumers to "phys"
suppliers is pretty well exercised. Most/all Android devices running
5.10+ kernels (including Pixel 6) use fw_devlink=on to be able to boot
properly.

So I'd be pretty confident in deleting the device_link_add/del() code
in drivers/pci/controller/dwc/pci-dra7xx.c. The device links should
already be there before the probe is even called.

Also, if you want to check if the device links (even the 1 phy one you
have) are being created, you can look at /sys/class/devlink to see the
list of all device links that are currently present. You can delete
the code and then use this to check too.

-Saravana

>
> --
> Luca