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

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Date:   Mon, 30 Aug 2021 09:27:26 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jeremy Linton <jeremy.linton@....com>,
        nicolas saenz julienne <nsaenz@...nel.org>,
        linux-pci@...r.kernel.org
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com, rjw@...ysocki.net,
        lenb@...nel.org, robh@...nel.org, kw@...ux.com,
        f.fainelli@...il.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 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.
-- 
Florian