[+cc linux-pci (please cc in the future since the bulk of this patch
is in drivers/pci/)]
On Wed, Jul 12, 2023 at 12:43:05AM +0800, Sui Jingfeng wrote:
> From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
>
> Currently, the strategy of selecting the default boot on a multiple video
> card coexistence system is not perfect. Potential problems are:
>
> 1) This function is a no-op on non-x86 architectures.
Which function in particular is a no-op for non-x86?
> 2) It does not take the PCI Bar may get relocated into consideration.
> 3) It is not effective for the PCI device without a dedicated VRAM Bar.
> 4) It is device-agnostic, thus it has to waste the effort to iterate all
> of the PCI Bar to find the VRAM aperture.
> 5) It has invented lots of methods to determine which one is the default
> boot device, but this is still a policy because it doesn't give the
> user a choice to override.
I don't think we need a list of *potential* problems. We need an
example of the specific problem this will solve, i.e., what currently
does not work?
The drm/ast and maybe drm/loongson patches are the only ones that use
the new callback, so I assume there are real problems with those
drivers.
CONFIG_DRM_AST is a tristate. We're talking about identifying the
boot-time console device. So if CONFIG_DRM_AST=m, I guess we don't
get the benefit of the new callback unless the module gets loaded?
> Also honor the comment: "Clients have *TWO* callback mechanisms they
> can use"
This refers to the existing vga_client_register() function comment:
* vga_client_register - register or unregister a VGA arbitration client
* @pdev: pci device of the VGA client
* @set_decode: vga decode change callback
*
* Clients have two callback mechanisms they can use.
*
* @set_decode callback: If a client can disable its GPU VGA resource, it
* will get a callback from this to set the encode/decode state.
and the fact that struct vga_device currently only contains *one*
callback function pointer:
unsigned int (*set_decode)(struct pci_dev *pdev, bool decode);
Adding the .is_primary_gpu() callback does mean there will now be two
callbacks, as the comment says, but I think it's just confusing to
mention this in the commit log, so I would just remove it.
> @@ -1509,13 +1543,24 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
> * cases of hotplugable vga cards.
> */
>
> - if (action == BUS_NOTIFY_ADD_DEVICE)
> + switch (action) {
> + case BUS_NOTIFY_ADD_DEVICE:
> notify = vga_arbiter_add_pci_device(pdev);
> - else if (action == BUS_NOTIFY_DEL_DEVICE)
> + if (notify)
> + vga_arbiter_notify_clients();
> + break;
> + case BUS_NOTIFY_DEL_DEVICE:
> notify = vga_arbiter_del_pci_device(pdev);
> + if (notify)
> + vga_arbiter_notify_clients();
> + break;
> + case BUS_NOTIFY_BOUND_DRIVER:
> + vga_arbiter_do_arbitration(pdev);
> + break;
> + default:
> + break;
> + }
Changing from if/else to switch makes the patch bigger than necessary
for no real benefit and obscures what is really changing.
Bjorn
