Re: [PATCH v2] efi: arm: defer probe of PCIe backed efifb on DT systems

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Tue, 24 Dec 2019 at 05:41, Saravana Kannan <saravanak@google.com> wrote:
>
> From: Ard Biesheuvel <ardb@kernel.org>
>
> The new of_devlink support breaks PCIe probing on ARM platforms booting
> via UEFI if the firmware exposes a EFI framebuffer that is backed by a
> PCI device. The reason is that the probing order gets reversed,
> resulting in a resource conflict on the framebuffer memory window when
> the PCIe probes last, causing it to give up entirely.
>
> Given that we rely on PCI quirks to deal with EFI framebuffers that get
> moved around in memory, we cannot simply drop the memory reservation, so
> instead, let's use the device link infrastructure to register this
> dependency, and force the probing to occur in the expected order.
>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> Co-developed-by: Saravana Kannan <saravanak@google.com>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>
> Hi Ard,
>
> I compile tested it and I think it should work. If you can actually run
> and test it, that'd be nice.
>
> You can also optimize find_pci_overlap_node() by caching the result if
> you think that's necessary.
>
> Right now this code will run always just like your code did. But once I
> rename of_devlink to fw_devlink, this code won't be run if fw_devlink is
> disabled.
>
> v1 -> v2:
> - Rewrote the device linking part to not depend on initcall ordering
>
>  drivers/firmware/efi/arm-init.c | 106 ++++++++++++++++++++++++++++++--
>  1 file changed, 102 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/firmware/efi/arm-init.c b/drivers/firmware/efi/arm-init.c
> index 904fa09e6a6b..8b789ff83af0 100644
> --- a/drivers/firmware/efi/arm-init.c
> +++ b/drivers/firmware/efi/arm-init.c
> @@ -10,10 +10,12 @@
>  #define pr_fmt(fmt)    "efi: " fmt
>
>  #include <linux/efi.h>
> +#include <linux/fwnode.h>
>  #include <linux/init.h>
>  #include <linux/memblock.h>
>  #include <linux/mm_types.h>
>  #include <linux/of.h>
> +#include <linux/of_address.h>
>  #include <linux/of_fdt.h>
>  #include <linux/platform_device.h>
>  #include <linux/screen_info.h>
> @@ -276,15 +278,111 @@ void __init efi_init(void)
>                 efi_memmap_unmap();
>  }
>
> +static bool efifb_overlaps_pci_range(const struct of_pci_range *range)
> +{
> +       u64 fb_base = screen_info.lfb_base;
> +
> +       if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> +               fb_base |= (u64)(unsigned long)screen_info.ext_lfb_base << 32;
> +
> +       return fb_base >= range->cpu_addr &&
> +              fb_base < (range->cpu_addr + range->size);
> +}
> +
> +static struct device_node *find_pci_overlap_node(void)
> +{
> +       struct device_node *np;
> +
> +       for_each_node_by_type(np, "pci") {
> +               struct of_pci_range_parser parser;
> +               struct of_pci_range range;
> +               int err;
> +
> +               err = of_pci_range_parser_init(&parser, np);
> +               if (err) {
> +                       pr_warn("of_pci_range_parser_init() failed: %d\n", err);
> +                       continue;
> +               }
> +
> +               for_each_of_pci_range(&parser, &range)
> +                       if (efifb_overlaps_pci_range(&range))
> +                               return np;
> +       }
> +       return NULL;
> +}
> +
> +/*
> + * If the efifb framebuffer is backed by a PCI graphics controller, we have
> + * to ensure that this relation is expressed using a device link when
> + * running in DT mode, or the probe order may be reversed, resulting in a
> + * resource reservation conflict on the memory window that the efifb
> + * framebuffer steals from the PCIe host bridge.
> + */
> +static int efifb_add_links(const struct fwnode_handle *fwnode,
> +                          struct device *dev)
> +{
> +       struct device_node *sup_np;
> +       struct device *sup_dev;
> +
> +       sup_np = find_pci_overlap_node();
> +
> +       /*
> +        * If there's no PCI graphics controller backing the efifb, we are
> +        * done here.
> +        */
> +       if (!sup_np)
> +               return 0;
> +
> +       sup_dev = get_dev_from_fwnode(&sup_np->fwnode);
> +       of_node_put(sup_np);
> +
> +       /*
> +        * Return -ENODEV if the PCI graphics controller device hasn't been
> +        * registered yet.  This ensures that efifb isn't allowed to probe
> +        * and this function is retried again when new devices are
> +        * registered.
> +        */
> +       if (!sup_dev)
> +               return -ENODEV;
> +
> +       /*
> +        * If this fails, retrying this function at a later point won't
> +        * change anything. So, don't return an error after this.
> +        */
> +       if (!device_link_add(dev, sup_dev, 0))
> +               dev_warn(dev, "device_link_add() failed\n");
> +
> +       put_device(sup_dev);
> +
> +       return 0;
> +}
> +
> +static struct fwnode_operations efifb_fwnode_ops = {

Please make this const

> +       .add_links = efifb_add_links,
> +};
> +
> +static struct fwnode_handle efifb_fwnode = {
> +       .ops = &efifb_fwnode_ops,
> +};
> +
>  static int __init register_gop_device(void)
>  {
> -       void *pd;
> +       struct platform_device *pd;
> +       int err;
>
>         if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI)
>                 return 0;
>
> -       pd = platform_device_register_data(NULL, "efi-framebuffer", 0,
> -                                          &screen_info, sizeof(screen_info));
> -       return PTR_ERR_OR_ZERO(pd);
> +       pd = platform_device_alloc("efi-framebuffer", 0);
> +       if (!pd)
> +               return -ENOMEM;
> +

Add

  if (IS_ENABLED(CONFIG_PCI))

here

> +       pd->dev.fwnode = &efifb_fwnode;
> +
> +       err = platform_device_add_data(pd, &screen_info, sizeof(screen_info));
> +       if (err)
> +               return err;
> +
> +       return platform_device_add(pd);
>  }
>  subsys_initcall(register_gop_device);
> --
> 2.24.1.735.g03f4e72817-goog
>

With the changes above

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

but it still needs testing as well.