linux-kernel - Re: [PATCH 2/4] cxl/mem: Reserve all device regions at once

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Date:   Wed, 19 May 2021 18:00:51 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Weiny, Ira" <ira.weiny@...el.com>
Cc:     Ben Widawsky <ben.widawsky@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-cxl@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] cxl/mem: Reserve all device regions at once

On Thu, May 6, 2021 at 3:37 PM <ira.weiny@...el.com> wrote:
>
> From: Ira Weiny <ira.weiny@...el.com>
>
> In order to remap individual register sets each bar region must be
> reserved prior to mapping.  Because the details of individual register
> sets are contained within the BARs themselves, the bar must be mapped 2
> times, once to extract this information and a second time for each
> register set.
>
> Rather than attempt to reserve each BAR individually and track if that
> bar has been reserved.  Open code pcim_iomap_regions() by first
> reserving all memory regions on the device and then mapping the bars
> individually as needed.
>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  drivers/cxl/pci.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 191603b4e10b..40016709b310 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -926,9 +926,9 @@ static void __iomem *cxl_mem_map_regblock(struct cxl_mem *cxlm, u32 reg_lo, u32
>  {
>         struct pci_dev *pdev = cxlm->pdev;
>         struct device *dev = &pdev->dev;
> +       void __iomem *rc;
>         u64 offset;
>         u8 bar;
> -       int rc;
>
>         offset = ((u64)reg_hi << 32) | (reg_lo & CXL_REGLOC_ADDR_MASK);
>         bar = FIELD_GET(CXL_REGLOC_BIR_MASK, reg_lo);
> @@ -940,13 +940,14 @@ static void __iomem *cxl_mem_map_regblock(struct cxl_mem *cxlm, u32 reg_lo, u32
>                 return (void __iomem *)ERR_PTR(-ENXIO);
>         }
>
> -       rc = pcim_iomap_regions(pdev, BIT(bar), pci_name(pdev));
> -       if (rc) {
> +       rc = pcim_iomap(pdev, bar, 0);

It is odd that the temporary region pinning uses non-pcim, but the
temporary mapping using pcim.

> +       if (!rc) {
>                 dev_err(dev, "failed to map registers\n");
> -               return (void __iomem *)ERR_PTR(rc);
> +               return (void __iomem *)ERR_PTR(-ENOMEM);

I think since this support is a bug/compatibility fix it should
probably be rebased to current cxl.git#next. If you still end up
needing to return an __iomem ERR_PTR() then use IOMEM_ERR_PTR.

>         }
>
> -       dev_dbg(dev, "Mapped CXL Memory Device resource\n");
> +       dev_dbg(dev, "Mapped CXL Memory Device resource bar %u @ 0x%llx\n",

s/0x%llx/%#llx/

> +               bar, offset);
>
>         return pcim_iomap_table(pdev)[bar] + offset;
>  }
> @@ -999,6 +1000,9 @@ static int cxl_mem_setup_regs(struct cxl_mem *cxlm)
>                 return -ENXIO;
>         }
>
> +       if (pci_request_mem_regions(pdev, pci_name(pdev)))

This tells me this patch is too fine grained and can't stand alone
because it is missing the corresponding call to
pci_release_mem_regions(). Ideally this would be kept in the same
scope as the temporary io mapping.

> +               return -ENODEV;
> +
>         /* Get the size of the Register Locator DVSEC */
>         pci_read_config_dword(pdev, regloc + PCI_DVSEC_HEADER1, &regloc_size);
>         regloc_size = FIELD_GET(PCI_DVSEC_HEADER1_LENGTH_MASK, regloc_size);
> --
> 2.28.0.rc0.12.gb6a658bd00c9
>