linux-kernel - Re: [PATCH RESEND v4 02/15] PCI: dwc: Detect iATU settings after getting "addr

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Message-ID: <20220728143825.GA298132@bhelgaas>
Date:   Thu, 28 Jul 2022 09:38:25 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Frank Li <Frank.Li@....com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND v4 02/15] PCI: dwc: Detect iATU settings after
 getting "addr_space" resource

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@...kalelectronics.ru>
> Reviewed-by: Rob Herring <robh@...nel.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
>