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

Florian Fainelli
2021-08-30T16:27:49Z

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