[PATCH v1] ARM: pci: add call to pcie_bus_configure_settings()

[Bjorn Helgaas]

On Thu, Jul 16, 2015 at 2:13 PM, Murali Karicheri <m-karicheri2 at ti.com> wrote:
> On 05/16/2015 10:02 AM, Bjorn Helgaas wrote:
>>
>> On Wed, May 28, 2014 at 01:14:53PM -0400, Murali Karicheri wrote:
>>>
>>> Call pcie_bus_configure_settings on ARM, like for other platforms.
>>> pcie_bus_configure_settings makes sure the MPS across the bus is
>>> uniform and provides the ability to tune the MRSS and MPS to higher
>>> performance values. This is particularly important for embedded where
>>> there is no firmware to program these PCI-E settings for the OS.
>>>
>>> Signed-off-by: Murali Karicheri <m-karicheri2 at ti.com>
>>>
>>> CC: Russell King <linux at arm.linux.org.uk>
>>> CC: Bjorn Helgaas <bhelgaas at google.com>
>>> CC: Arnd Bergmann <arnd at arndb.de>
>>> CC: Jason Gunthorpe <jgunthorpe at obsidianresearch.com>
>>> CC: Santosh Shilimkar <santosh.shilimkar at ti.com>
>>>
>>> ---
>>>   - Fixed comments against initial version
>>>   arch/arm/kernel/bios32.c |   12 ++++++++++++
>>>   1 file changed, 12 insertions(+)
>>>
>>> diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
>>> index 16d43cd..17a26c1 100644
>>> --- a/arch/arm/kernel/bios32.c
>>> +++ b/arch/arm/kernel/bios32.c
>>> @@ -545,6 +545,18 @@ void pci_common_init_dev(struct device *parent,
>>> struct hw_pci *hw)
>>>                  */
>>>                 pci_bus_add_devices(bus);
>>>         }
>>> +
>>> +       list_for_each_entry(sys, &head, node) {
>>> +               struct pci_bus *bus = sys->bus;
>>> +
>>> +               /* Configure PCI Express settings */
>>> +               if (bus && !pci_has_flag(PCI_PROBE_ONLY)) {
>>> +                       struct pci_bus *child;
>>> +
>>> +                       list_for_each_entry(child, &bus->children, node)
>>> +                               pcie_bus_configure_settings(child);
>>
>>
>> This patch (8b5742ad156d ("ARM/PCI: Call pcie_bus_configure_settings() to
>> set MPS")) has been upstream since v3.16-rc1, but I think we goofed.
>>
>> The MPS configuration should be done *before* pci_bus_add_devices().
>> After
>> pci_bus_add_devices(), drivers may be bound to devices, and the PCI core
>> shouldn't touch device configuration while a driver owns the device.
>>
>> Looking at the code, it seems like it would have been simpler to do this
>> in
>> the existing loop:
>>
>>    list_for_each_entry(sys, &head, node) {
>>      struct pci_bus *bus = sys->bus;
>>
>>      if (bus && !pci_has_flag(PCI_PROBE_ONLY)) {
>>        pci_bus_size_bridges(bus);
>>        pci_bus_assign_resources(bus);
>>        list_for_each_entry(child, &bus->children, node)
>>          pcie_bus_configure_settings(child);
>>      }
>>
>>      pci_bus_add_devices(bus);
>>    }
>>
>> so maybe there's some reason I'm not aware of for not doing it that way?
>
>
> Bjorn,
>
> This one has escaped my radar and I found it recently while I was searching
> for something else. I can't recall why this was not done this way. However I
> have tried the below code on Keystone and it works fine.
>
> diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
> index fcbbbb1..17efde7 100644
> --- a/arch/arm/kernel/bios32.c
> +++ b/arch/arm/kernel/bios32.c
> @@ -520,7 +520,8 @@ void pci_common_init_dev(struct device *parent, struct
> hw_pci *hw)
>         list_for_each_entry(sys, &head, node) {
>                 struct pci_bus *bus = sys->bus;
>
> -               if (!pci_has_flag(PCI_PROBE_ONLY)) {
> +               if (bus && !pci_has_flag(PCI_PROBE_ONLY)) {
> +                       struct pci_bus *child;
>                         /*
>                          * Size the bridge windows.
>                          */
> @@ -530,25 +531,15 @@ void pci_common_init_dev(struct device *parent, struct
> hw_pci *hw)
>                          * Assign resources.
>                          */
>                         pci_bus_assign_resources(bus);
> -               }
>
> +                       list_for_each_entry(child, &bus->children, node)
> +                               pcie_bus_configure_settings(child);
> +               }
>                 /*
>                  * Tell drivers about devices found.
>                  */
>                 pci_bus_add_devices(bus);
>         }
> -
> -       list_for_each_entry(sys, &head, node) {
> -               struct pci_bus *bus = sys->bus;
> -
> -               /* Configure PCI Express settings */
> -               if (bus && !pci_has_flag(PCI_PROBE_ONLY)) {
> -                       struct pci_bus *child;
> -
> -                       list_for_each_entry(child, &bus->children, node)
> -                               pcie_bus_configure_settings(child);
> -               }
> -       }
>  }
>
> The SATA comes up fine and ahci is able to override the mrrs value as shown
> by the log below.
>
> [    1.581526] ahci 0001:01:00.0: limiting MRRS to 256
> [    1.586521] ahci 0001:01:00.0: AHCI 0001.0000 32 slots 2 ports 6 Gbps 0x3
> impl SATA mode
> [    1.594604] ahci 0001:01:00.0: flags: 64bit ncq sntf led only pmp fbs pio
> slum part sxs
> [    1.603772] scsi host0: ahci
> [    1.606976] scsi host1: ahci
> [
>
> If you are fine, I can send a patch for this. Please confirm.

Yes, please!  I think the existing code that calls
pci_bus_add_devices() before configuring MPS is wrong, because MPS
should be configured before drivers can claim the device.

Bjorn