Re: [PATCH RESEND v4 02/15] PCI: dwc: Detect iATU settings after getting "addr_space" resource

Bjorn Helgaas
2022-07-28T14:40:59Z

On Fri, Jun 24, 2022 at 05:39:34PM +0300, Serge Semin wrote:
> The iATU detection procedure was introduced in the commit 281f1f99cf3a
> ("PCI: dwc: Detect number of iATU windows"). A bit later the procedure
> execution was moved to Host/EP-specific methods in the framework of commit
> 8bcca2658558 ("PCI: dwc: Move iATU detection earlier"). The later
> modification wasn't done in the most optimal way since the "addr_space"
> CSR region resource doesn't depend on anything detected in the
> dw_pcie_iatu_detect() method. Thus the detection can be postponed to be
> executed after the resource request which can fail and make the detection
> pointless. It will be also helpful for the dw_pcie_ep_init() method
> readability since we are about to add the IP-core version and eDMA module
> (a bit later) detection procedures.

The patch is fine, but IMO the commit log is overkill. It's enough to
say that we do some work (dw_pcie_iatu_detect()) earlier than
necessary, so we can move it later. All the history makes it seem
like this is more complicated than it really is.

Something like this is enough:

Previously, dw_pcie_ep_init() did:

dw_pcie_iatu_detect(pci);
res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "addr_space");
if (!res)
return -EINVAL;

The platform_get_resource_byname() can fail, and dw_pcie_iatu_detect()
doesn't depend on the "addr_space" resource, so delay it until afterwards,
i.e.,

platform_get_resource_byname(pdev, IORESOURCE_MEM, "addr_space");
dw_pcie_iatu_detect(pci);

No need to repost for this.

> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> Reviewed-by: Rob Herring <robh@kernel.org>
>
> ---
>
> Changelog v2:
> - This is a new patch added on v2 iteration of the series.
> ---
> drivers/pci/controller/dwc/pcie-designware-ep.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-ep.c b/drivers/pci/controller/dwc/pcie-designware-ep.c
> index 15b8059544e3..1e35542d6f72 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> @@ -704,8 +704,6 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> }
> }
>
> - dw_pcie_iatu_detect(pci);
> -
> res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "addr_space");
> if (!res)
> return -EINVAL;
> @@ -713,6 +711,8 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
> ep->phys_base = res->start;
> ep->addr_size = resource_size(res);
>
> + dw_pcie_iatu_detect(pci);
> +
> ep->ib_window_map = devm_kcalloc(dev,
> BITS_TO_LONGS(pci->num_ib_windows),
> sizeof(long),
> --
> 2.35.1
>