linux-kernel - Re: [PATCH] Revert "PCI: dwc: Wait for link up only if link is started"

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Date:   Mon, 10 Jul 2023 22:12:07 +0530
From:   Ajay Agarwal <ajayagarwal@...gle.com>
To:     Johan Hovold <johan@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        Sajid Dalvi <sdalvi@...gle.com>
Subject: Re: [PATCH] Revert "PCI: dwc: Wait for link up only if link is
 started"

On Mon, Jul 10, 2023 at 09:51:22PM +0530, Ajay Agarwal wrote:
> On Fri, Jul 07, 2023 at 02:47:56PM +0200, Johan Hovold wrote:
> > On Thu, Jul 06, 2023 at 06:28:11PM +0530, Manivannan Sadhasivam wrote:
> > > On Thu, Jul 06, 2023 at 10:26:10AM +0200, Johan Hovold wrote:
> > 
> > > > Finally, note that the intel-gw driver is the only driver currently not
> > > > providing a start_link callback and instead starts the link in its
> > > > host_init callback, and which may avoid an additional one-second timeout
> > > > during probe by making the link-up wait conditional. If anyone cares,
> > > > that can be done in a follow-up patch with a proper motivation.
> > 
> > > The offending commit is bogus since it makes the intel-gw _special_ w.r.t
> > > waiting for the link up. Most of the drivers call dw_pcie_host_init() during the
> > > probe time and they all have to wait for 1 sec if the slot is empty.
> Mani, can you please explain how my commit made the intel-gw driver
> special? The intel driver actually fails the dw_pcie_host_init if the
> link does not come up. That was my motivation behind adding the fail
> logic in the core driver as well.
> > 
> > Just to clarify, the intel-gw driver starts the link and waits for link
> > up in its host_init() callback, which is called during probe. That wait
> > could possibly just be dropped in favour of the one in
> > dw_pcie_host_init() and/or the driver could be reworked to implement
> > start_link().
> > 
> > Either way, the call in dw_pcie_host_init() will only add an additional
> > 1 second delay in cases where the link did *not* come up.
> > 
> > > As Johan noted, intel-gw should make use of the async probe to avoid the boot
> > > delay instead of adding a special case.
> > 
> > Indeed.
> > 
> > Johan
> Johan, Mani
> My apologies for adding this regression in some of the SOCs.
> May I suggest to keep my patch and make the following change instead?
> This shall keep the existing behavior as is, and save the boot time
> for drivers that do not define the start_link()?
> 
> ```
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index cf61733bf78d..af6a7cd060b1 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -492,11 +492,8 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>                 if (ret)
>                         goto err_remove_edma;
> 
> -               if (pci->ops && pci->ops->start_link) {
> -                       ret = dw_pcie_wait_for_link(pci);
> -                       if (ret)
> -                               goto err_stop_link;
> -               }
> +               if (pci->ops && pci->ops->start_link)
> +                       dw_pcie_wait_for_link(pci);
>         }
> 
>         bridge->sysdata = pp;
> ```
I just realized that Fabio pushed exactly the same patch as I suggested
here:
https://lore.kernel.org/all/20230704122635.1362156-1-festevam@gmail.com/.
I think it is better we take it instead of reverting my commit.