linux-kernel - Re: [PATCH 07/15] PCI: brcmstb: Add control of rescal reset

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Date:   Thu, 21 May 2020 17:48:15 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Philipp Zabel <pza@...gutronix.de>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/15] PCI: brcmstb: Add control of rescal reset

On Wed, May 20, 2020 at 3:27 AM Philipp Zabel <pza@...gutronix.de> wrote:
>
> Hi Jim,
>
> On Tue, May 19, 2020 at 04:34:05PM -0400, Jim Quinlan wrote:
> > From: Jim Quinlan <jquinlan@...adcom.com>
> >
> > Some STB chips have a special purpose reset controller named
> > RESCAL (reset calibration).  This commit adds the control
> > of RESCAL as well as the ability to start and stop its
> > operation for PCIe HW.
> >
> > Signed-off-by: Jim Quinlan <jquinlan@...adcom.com>
> > ---
> >  drivers/pci/controller/pcie-brcmstb.c | 81 ++++++++++++++++++++++++++-
> >  1 file changed, 80 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> > index 2c470104ba38..0787e8f6f7e5 100644
> > --- a/drivers/pci/controller/pcie-brcmstb.c
> > +++ b/drivers/pci/controller/pcie-brcmstb.c
> [...]
> > @@ -1100,6 +1164,21 @@ static int brcm_pcie_probe(struct platform_device *pdev)
> >               dev_err(&pdev->dev, "could not enable clock\n");
> >               return ret;
> >       }
> > +     pcie->rescal = devm_reset_control_get_shared(&pdev->dev, "rescal");
> > +     if (IS_ERR(pcie->rescal)) {
> > +             if (PTR_ERR(pcie->rescal) == -EPROBE_DEFER)
> > +                     return -EPROBE_DEFER;
> > +             pcie->rescal = NULL;
>
> This is effectively an optional reset control, so it is better to use:
> ↵
>         pcie->rescal = devm_reset_control_get_optional_shared(&pdev->dev,
>                                                               "rescal");↵
>         if (IS_ERR(pcie->rescal))
>                 return PTR_ERR(pcie->rescal);
>
> > +     } else {
> > +             ret = reset_control_deassert(pcie->rescal);
> > +             if (ret)
> > +                     dev_err(&pdev->dev, "failed to deassert 'rescal'\n");
> > +     }
>
> reset_control_* can handle rstc == NULL parameters for optional reset
> controls, so this can be done unconditionally:
>
>         ret = reset_control_deassert(pcie->rescal);↵
>         if (ret)↵
>                 dev_err(&pdev->dev, "failed to deassert 'rescal'\n");↵
>
> Is rescal handled by the reset-brcmstb-rescal driver? Since that only
> implements the .reset op, I would expect reset_control_reset() here.
Where exactly?  "reset.h" says that "Calling reset_control_rese()t is
not allowed on a shared reset control." so I'm not sure why  you would
want me to invoke it.
> Otherwise this looks like it'd be missing a reset_control_assert in
> remove.
I can add this.
Thanks,
Jim
>
> regards
> Philipp