linux-kernel - Re: dwc: tegra194: issue with card containing a bridge

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Date:   Fri, 18 Dec 2020 11:12:21 +0100
From:   Mian Yousaf Kaukab <ykaukab@...e.de>
To:     Rob Herring <robh@...nel.org>
Cc:     Vidya Sagar <vidyas@...dia.com>, lorenzo.pieralisi@....com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: dwc: tegra194: issue with card containing a bridge

On Thu, Dec 17, 2020 at 06:06:35PM +0100, Mian Yousaf Kaukab wrote:
> On Thu, Dec 17, 2020 at 08:58:57AM -0600, Rob Herring wrote:
> > On Tue, Dec 15, 2020 at 09:52:35PM +0100, Mian Yousaf Kaukab wrote:
> > > On Tue, Dec 15, 2020 at 09:41:47AM -0600, Rob Herring wrote:
> > > > On Tue, Dec 15, 2020 at 02:25:04PM +0100, Mian Yousaf Kaukab wrote:
> > > > > On Tue, Dec 15, 2020 at 05:45:59PM +0530, Vidya Sagar wrote:
> > > > > > Thanks Mian for bringing it to our notice.
> > > > > > Have you tried removing the dw_pcie_setup_rc(pp); call from pcie-tegra194.c
> > > > > > file on top of linux-next? and does that solve the issue?
> > > > > > 
> > > > > > diff --git a/drivers/pci/controller/dwc/pcie-tegra194.c
> > > > > > b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > > > > index 5597b2a49598..1c9e9c054592 100644
> > > > > > --- a/drivers/pci/controller/dwc/pcie-tegra194.c
> > > > > > +++ b/drivers/pci/controller/dwc/pcie-tegra194.c
> > > > > > @@ -907,7 +907,7 @@ static void tegra_pcie_prepare_host(struct pcie_port
> > > > > > *pp)
> > > > > >                 dw_pcie_writel_dbi(pci, CFG_TIMER_CTRL_MAX_FUNC_NUM_OFF,
> > > > > > val);
> > > > > >         }
> > > > > > 
> > > > > > -       dw_pcie_setup_rc(pp);
> > > > > > +       //dw_pcie_setup_rc(pp);
> > > > > I still see the same issue with this change.
> > > > > Reverting b9ac0f9dc8ea works though.
> > > > > > 
> > > > > >         clk_set_rate(pcie->core_clk, GEN4_CORE_CLK_FREQ);
> > > > > > 
> > > > > > I took a quick look at the dw_pcie_setup_rc() implementation and I'm not
> > > > > > sure why calling it second time should create any issue for the enumeration
> > > > > > of devices behind a switch. Perhaps I need to spend more time to debug that
> > > > > > part.
> > > > > > In any case, since dw_pcie_setup_rc() is already part of
> > > > > > dw_pcie_host_init(), I think it can be removed from
> > > > > > tegra_pcie_prepare_host() implemention.
> > > > 
> > > > I think the 2nd time is making the link go down is my guess. Tegra was 
> > > > odd in that its start/stop link functions don't do link handling, so I 
> > > > didn't implement those functions and left the link handling in the Tegra 
> > > > driver.
> > > > 
> > > > Can you try the below patch. It needs some more work as it breaks 
> > > > endpoint mode.
> > 
> > [...]
> > 
> > > Boot is ok with this patch. Some improvement in lspci as well:
> > 
> > Some improvement? Meaning not completely working still?
> > 
> > > # lspci
> > > 0001:00:00.0 PCI bridge: NVIDIA Corporation Device 1ad2 (rev a1)
> > > 0001:01:00.0 SATA controller: Marvell Technology Group Ltd. Device 9171 (rev 13)
> > > 0005:00:00.0 PCI bridge: NVIDIA Corporation Device 1ad0 (rev a1)
> > > 0005:01:00.0 PCI bridge: PLX Technology, Inc. Device 3380 (rev ab)
> > 
> > This patch was closer to the original flow, but would not have worked if 
> > DLFE disabled mode was needed.
> > 
> > Please give this patch a try:
> Thank you for the patch! Initial results with it looks very promising.
> I’ll get back to you tomorrow after running a few more tests.
Rob, thank you for your efforts! This patch fixed the issue I was seeing. FWIW:

Tested-by: Mian Yousaf Kaukab <ykaukab@...e.de>

BR,
Yousaf