Re: [PATCH] pci/pcie: Avoid unnecessary PCIe link retrains

From: Kenji Kaneshige
Date: Thu Nov 05 2009 - 20:15:32 EST

Bjorn Helgaas wrote:
On Thursday 05 November 2009 12:07:07 pm Matthew Wilcox wrote:
On Thu, Nov 05, 2009 at 12:59:25PM -0600, Bjorn Helgaas wrote:
Here's another possibility, the idea being to collect all the PCIe
stuff in one place. This would require a lot of changes in the PCIe
driver code, but most of them would be trivial.
I don't like the idea of kmallocing a 6- or 10-byte data structure
... better to keep it in the pci_dev. Maybe embedding a pcie_dev inside
the pci_dev would be a good idea, but unless there're more things to
move to it, this seems like a net loss to me.

That's true, it's not worth it for such a small structure. I figured
there would probably be more PCIe-related stuff that could go there,
e.g., embedding the link_state directly. But I haven't looked to
see whether there actually is enough PCIe stuff to make it worthwhile.

In my understanding, there are the following PCIe specific data in
struct pci_dev. It is not many.

u8 pcie_cap; *I added this time
u8 pcie_type;
struct pcie_link_state *link_state;
unsigned int ari_enabled:1;
unsigned int is_pcie:1; *No longer needed and will be removed.
unsigned int aer_firmware_first:1;

How about keeping cap offset in pci_dev so far and introducing the
following wrapper function?

static inline pcie_cap(struct pci_dev *pdev)
return pdev->pcie_cap;

When we actually need a new data structure for PCIe-related stuff in the
future, all we need to do would be changing this wrapper like below.

static inline pcie_cap(struct pci_dev *pdev)
struct pcie_dev *pcie = pdev->pcie;
if (pcie)
return pcie->cap;
return 0;

Kenji Kaneshige

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