linux-kernel - Re: [PATCH v3 2/4] PCI: brcmstb: Add ACPI config space quirk

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Date:   Mon, 30 Aug 2021 19:17:32 +0200
From:   nicolas saenz julienne <nsaenz@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Jeremy Linton <jeremy.linton@....com>,
        linux-pci@...r.kernel.org
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com, rjw@...ysocki.net,
        lenb@...nel.org, robh@...nel.org, kw@...ux.com,
        bcm-kernel-feedback-list@...adcom.com, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] PCI: brcmstb: Add ACPI config space quirk

On Mon, 2021-08-30 at 09:27 -0700, Florian Fainelli wrote:
> 
> On 8/30/2021 9:23 AM, Jeremy Linton wrote:
> > Hi,
> > 
> > On 8/30/21 3:36 AM, nicolas saenz julienne wrote:
> > > Hi Jeremy,
> > > sorry for the late reply, I've been on vacation.
> > > 
> > > On Thu, 2021-08-26 at 02:15 -0500, Jeremy Linton wrote:
> > > 
> > > [...]
> > > 
> > > > +static void __iomem *brcm_pcie_map_conf2(struct pci_bus *bus,
> > > > +                    unsigned int devfn, int where)
> > > > +{
> > > > +    struct pci_config_window *cfg = bus->sysdata;
> > > > +    void __iomem *base = cfg->win;
> > > > +    int idx;
> > > > +    u32 up;
> > > > +
> > > > +    /* Accesses to the RC go right to the RC registers if slot==0 */
> > > > +    if (pci_is_root_bus(bus))
> > > > +        return PCI_SLOT(devfn) ? NULL : base + where;
> > > > +
> > > > +    /*
> > > > +     * Assure the link is up before sending requests downstream. 
> > > > This is done
> > > > +     * to avoid sending transactions to EPs that don't exist. Link flap
> > > > +     * conditions/etc make this race more probable. The resulting 
> > > > unrecoverable
> > > > +     * SERRORs will result in the machine crashing.
> > > > +     */
> > > > +    up = readl(base + PCIE_MISC_PCIE_STATUS);
> > > > +    if (!(up & PCIE_MISC_PCIE_STATUS_PCIE_DL_ACTIVE_MASK))
> > > > +        return NULL;
> > > > +
> > > > +    if (!(up & PCIE_MISC_PCIE_STATUS_PCIE_PHYLINKUP_MASK))
> > > > +        return NULL;
> > > 
> > > Couldn't this be integrated in the original brcm_pcie_map_conf()? IIUC 
> > > there is
> > > nothing ACPI specific about it. It'd also make for less code duplication.
> > 
> > That is where I started with this, but it wasn't the linkup check/etc 
> > which caused me to hoist it but the fact that if ACPI quirks are enabled 
> > they end up statically built into the kernel. While if this host bridge 
> > is enabled, it can end up being a module, and the resulting mess I 
> > created trying to satisfy the CONFIG variations. I'm not much of a fan 
> > of copy/paste programming, but that IMHO ended up being the cleanest here.
> > 
> 
> Agreed, the open coding that is being done is reasonable IHMO, although 
> we may have to update the link up code in both pcie-brcmstb.c and this 
> file in the future if offsets/bits do change, nothing impossible though.

Fair enough.

Acked-by: Nicolas Saenz Julienne <nsaenz@...nel.org>

Regards,
Nicolas