[PATCH v3] efifb: avoid reconfiguration of BAR that covers the framebuffer
From: Sinan Kaya <hidden>
Date: 2017-03-22 19:57:56
Also in:
linux-efi, linux-pci
On 3/22/2017 3:52 PM, Ard Biesheuvel wrote:
On 22 March 2017 at 19:49, Sinan Kaya [off-list ref] wrote:quoted
On 3/22/2017 3:41 PM, Ard Biesheuvel wrote:quoted
quoted
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.
quoted
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.quoted
quoted
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?quoted
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.