Re: [PATCH v4 01/16] PCI: dwc: Add pcie_cap field and caching helper

[sashiko-bot@kernel.org]

> The DWC PCIe core and its platform drivers repeatedly call
> dw_pcie_find_capability(pci, PCI_CAP_ID_EXP) to obtain the offset of the
> PCI Express Capability structure. Besides being verbose, that performs a
> DBI read every time, including in paths that run repeatedly such as link
> up polling, suspend/resume and interrupt handlers.
> 
> Add a pcie_cap field to struct dw_pcie and a helper
> dw_pcie_get_pcie_cap() that performs the lookup on first use and caches
> the result for the subsequent calls.
> 
> The lookup is deliberately done lazily, at the first place that needs the
> offset, instead of at a fixed point during controller initialization.
> This guarantees that the DBI read happens exactly when the open coded
> dw_pcie_find_capability() call it replaces used to happen, so no DBI
> access can be made before the controller clocks, resets and power are
> [ ... ]
> cannot happen on real DWC hardware, where the PCI Express Capability is
> mandatory, so a negative result is not cached separately: it only causes
> the search to be repeated, which does not affect correctness.
> 
> Signed-off-by: Hans Zhang <18255117159@163.com>

Sashiko has reviewed this patch and found no issues.

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