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

Bjorn Helgaas
2015-07-16T19:36:24Z

On Thu, Jul 16, 2015 at 2:13 PM, Murali Karicheri <m-karicheri2@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@ti.com>
>>>
>>> CC: Russell King <linux@arm.linux.org.uk>
>>> CC: Bjorn Helgaas <bhelgaas@google.com>
>>> CC: Arnd Bergmann <arnd@arndb.de>
>>> CC: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
>>> CC: Santosh Shilimkar <santosh.shilimkar@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