On 3/22/2017 3:52 PM, Ard Biesheuvel wrote: > On 22 March 2017 at 19:49, Sinan Kaya <okaya@xxxxxxxxxxxxxx> wrote: >> On 3/22/2017 3:41 PM, Ard Biesheuvel wrote: >>>> As far as I know, kernel honors resource assignments done by the UEFI BIOS if >>>> they are correct. Kernel will reassign the resources only if something is wrong. >>>> >>> No, the kernel always reassigns all BARs on arm64. >> >> I think this is where the problem is. >> >> I'm not seeing this happen on QDF2400 which supports ACPI + UEFI BIOS >> combination only. >> >> I see that kernel honored the resources assigned by UEFI BIOS if I compare >> the BAR addresses. >> > > Well, if you are using the standard MdeModulePkg PciHostBridgeDxe > driver in UEFI, the logic is quite similar, and so you usually end up > with the same resource assignments. But the kernel does recompute them > from scratch, and ignores the existing configuration that is present > in the BARs Yes, standard stuff in UEFI. OK. That may explain what I'm seeing. > >> I see reassignment only when something is horribly broken. Then, there would >> be a bridge configuration invalid message in the boot log to confirm this. >> >>> >>>> Will this code break other platforms/architectures? >>>> >>> Which platforms/architectures are you referring to? EFIFB on a PCI >>> device is currently broken on arm64. >> >> In general or on your particular platform? >> >>> On x86, it works, given that BARs >>> are usually not reassigned, and so the patch should be a no-op in that >>> case (although I'd argue it is still an improvement to check whether >>> the device that owns the BAR actually has memory decoding enabled >>> before we attach the framebuffer driver to it) >>> >> >> I'm fine as long as it doesn't break anything. That's why, I'm asking. >> > > If you have working EFIFB on your platform, it works by accident. This > patch is needed to ensure that the BAR associated with the EFI > framebuffer is left untouched. > I never claimed that. I was just double checking your assumptions. I really don't like ARM64 specific PCI code in general. PCI doesn't care about CPU type. I hope to see this patch become part of common code. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
