[PATCH 1/3] pci_auto: Downgrade prefetch if necessary

[PATCH 1/3] pci_auto: Downgrade prefetch if necessary

[Patrick Rudolph]

Legacy PCI devices, like qemu's Bochs VGA device, are allowed to have
prefetchable 32-bit BARs, while PCIe devices are not allowed to have
32-bit prefetchable BARs. Typically prefetchable BARs are 64-bit and
typically the prefetch MMIO window is also 64-bit and placed above
4GiB, as it's the case on qemu sbsa-ref.

Currently the U-Boot code assumes that prefetchable BARs are
64-bit BARs and always tries to assign them into the prefetch
MMIO window.

When a 32-bit BAR is marked as prefetch, but the prefetch area is
not within the first 4GiB of the address space, then downgrade the
BAR and place it in the non-prefetch MMIO window.

For prefetch BARs there's no downside on being placed in non prefetch
MMIO areas, besides the possible slower performance when a driver tries
to map it Write-Combine.

TEST: Fixes pci_auto on QEMU sbsa-ref fails to autoconfigure BAR0.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
---
 drivers/pci/pci_auto.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci_auto.c b/drivers/pci/pci_auto.c
index 90f81886445..e68e31a8227 100644
--- a/drivers/pci/pci_auto.c
+++ b/drivers/pci/pci_auto.c
@@ -107,7 +107,8 @@ static void dm_pciauto_setup_device(struct udevice *dev,
 			}
 
 			if (prefetch &&
-			    (bar_response & PCI_BASE_ADDRESS_MEM_PREFETCH))
+			    (bar_response & PCI_BASE_ADDRESS_MEM_PREFETCH) &&
+			    (found_mem64 || prefetch->bus_lower < 0x100000000ULL))
 				bar_res = prefetch;
 			else
 				bar_res = mem;
-- 
2.48.1

[PATCH 2/3] emulation: qemu-sbsa: Select SYS_PCI_64BIT

[Patrick Rudolph]

qemu's sbsa-ref is always using a 64bit CPU and the PCI prefetch MMIO
window is located above 4GiB, thus always enable SYS_PCI_64BIT.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
---
 board/emulation/qemu-sbsa/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/board/emulation/qemu-sbsa/Kconfig b/board/emulation/qemu-sbsa/Kconfig
index 72c76b351fa..f4ad63e681c 100644
--- a/board/emulation/qemu-sbsa/Kconfig
+++ b/board/emulation/qemu-sbsa/Kconfig
@@ -33,6 +33,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	select OF_SEPARATE
 	select PCI
 	select PCIE_ECAM_GENERIC
+	select SYS_PCI_64BIT
 	select USB
 	select GIC_V3
 	select GIC_V3_ITS
-- 
2.48.1

[PATCH 3/3] emulation: qemu-sbsa: Enable PCI enumeration

[Patrick Rudolph]

Enable PCI enumeration by default to get the Bochs display driver up
and running before the boot medium is scanned.
This is just to enhance the user-experience while booting the machine.

TEST: U-Boot logo, version, log output and the U-Boot shell is visible
      on the display device.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
---
 board/emulation/qemu-sbsa/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/board/emulation/qemu-sbsa/Kconfig b/board/emulation/qemu-sbsa/Kconfig
index f4ad63e681c..728cecae6b3 100644
--- a/board/emulation/qemu-sbsa/Kconfig
+++ b/board/emulation/qemu-sbsa/Kconfig
@@ -49,6 +49,7 @@ config BOARD_SPECIFIC_OPTIONS # dummy
 	imply CFI_FLASH
 	imply SYS_MTDPARTS_RUNTIME
 	imply SET_DFU_ALT_INFO
+	imply PCI_INIT_R
 
 if DEBUG_UART
 
-- 
2.48.1

Re: [PATCH 1/3] pci_auto: Downgrade prefetch if necessary

[Tom Rini]

On Wed, 26 Feb 2025 14:56:42 +0100, Patrick Rudolph wrote:

> Legacy PCI devices, like qemu's Bochs VGA device, are allowed to have
> prefetchable 32-bit BARs, while PCIe devices are not allowed to have
> 32-bit prefetchable BARs. Typically prefetchable BARs are 64-bit and
> typically the prefetch MMIO window is also 64-bit and placed above
> 4GiB, as it's the case on qemu sbsa-ref.
> 
> Currently the U-Boot code assumes that prefetchable BARs are
> 64-bit BARs and always tries to assign them into the prefetch
> MMIO window.
> 
> [...]

Applied to u-boot/next, thanks!

[1/3] pci_auto: Downgrade prefetch if necessary
      commit: 699baa63ddcabe141adf3305d61f7b2a0d2de5db
[2/3] emulation: qemu-sbsa: Select SYS_PCI_64BIT
      commit: 0dbb770981d6acff3cc4921454403998dd5d0c92
[3/3] emulation: qemu-sbsa: Enable PCI enumeration
      commit: 6b9f4d0f7f070845133bcddf5e5c2dfedf32170b
-- 
Tom