Re: [PATCH] pcie: enable Extended tag field capability

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 18 Oct 2024 12:24:05 +0200
Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org> wrote:

> W dniu 17.10.2024 o 18:58, Michael S. Tsirkin pisze:
> >> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> >> index 4b2f0805c6..54c0f1ec67 100644
> >> --- a/hw/pci/pcie.c
> >> +++ b/hw/pci/pcie.c
> >> @@ -86,7 +86,8 @@ pcie_cap_v1_fill(PCIDevice *dev, uint8_t port, uint8_t type, uint8_t version)
> >>        * Specification, Revision 1.1., or subsequent PCI Express Base
> >>        * Specification revisions.
> >>        */
> >> -    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER);
> >> +    pci_set_long(exp_cap + PCI_EXP_DEVCAP, PCI_EXP_DEVCAP_RBER |
> >> +                 PCI_EXP_DEVCAP_EXT_TAG);
> >>   
> >>       pci_set_long(exp_cap + PCI_EXP_LNKCAP,
> >>                    (port << PCI_EXP_LNKCAP_PN_SHIFT) |  
> > 
> > We can't change capabilities unconditionally.
> > It needs at least a machine type compat thing.  
> 
> Started looking and wonder how to pass it from MachineClass level down 
> to pcie.c/pcie_cap_v1_fill() level.

see as an example:
  fa905f65c5549 hw/nvme: add machine compatibility parameter to enable msix exclusive bar
 
> hw/arm/sbsa-ref.c (the machine I know best) has create_pcie() which 
> allocates PCI_HOST_BRIDGE and then creates 2 pcie devices (default_nic 
> (e1000e) and bochs-display gfx).
> 
> If I add "pcie_uses_ext_tags = true" to SBSAMachineState then I need to 
> have it stored in PCIBus structure so pci_create_simple() will know. 
> This function would copy it into "dev" (PCIDevice) to make it pass to 
> pcie_cap_v1_fill() function.
> 
> But that's not right way because other PCIe devices are created in other 
> places.
> 
> Need to dig deeper.
>