[XS] Change in coreboot[main]: mb/qemu/fw_cfg: Support using DMA to select fw_cfg file

[Felix Singer (Code Review)]

Felix Singer has submitted this change. ( https://review.coreboot.org/c/coreboot/+/80365?usp=email )

Change subject: mb/qemu/fw_cfg: Support using DMA to select fw_cfg file
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mb/qemu/fw_cfg: Support using DMA to select fw_cfg file

Commit 8dc95ddbd4a935 ("emulation/qemu-i440fx: use fw_cfg_dma for
fw_cfg_read") adds DMA support to interface with the QEMU firmware
configuration device, and uses it to read from the "files" exposed by
the device. However, the file selection step still uses port-based IO.

Use DMA for fw_cfg file selection when possible, as a step towards
porting this driver to other architectures.

Change-Id: I46f9915e6df04d371c7084815f16034c7e9879d4
Signed-off-by: Alper Nebi Yasak 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80365
Tested-by: build bot (Jenkins) 
Reviewed-by: Martin L Roth 
Reviewed-by: Matt DeVillier 
Reviewed-by: Nico Huber 
Reviewed-by: Felix Singer 
---
M src/mainboard/emulation/qemu-i440fx/fw_cfg.c
1 file changed, 4 insertions(+), 1 deletion(-)

Approvals:
  Matt DeVillier: Looks good to me, approved
  build bot (Jenkins): Verified
  Nico Huber: Looks good to me, but someone else must approve
  Martin L Roth: Looks good to me, approved
  Felix Singer: Looks good to me, approved

diff --git a/src/mainboard/emulation/qemu-i440fx/fw_cfg.c b/src/mainboard/emulation/qemu-i440fx/fw_cfg.c
index a15773c..ad664a6 100644
--- a/src/mainboard/emulation/qemu-i440fx/fw_cfg.c
+++ b/src/mainboard/emulation/qemu-i440fx/fw_cfg.c
@@ -44,7 +44,10 @@

static void fw_cfg_select(uint16_t entry)
 {
-	outw(entry, FW_CFG_PORT_CTL);
+	if (fw_ver & FW_CFG_VERSION_DMA)
+		fw_cfg_dma(FW_CFG_DMA_CTL_SELECT | entry << 16, NULL, 0);
+	else
+		outw(entry, FW_CFG_PORT_CTL);
 }

static void fw_cfg_read(void *dst, int dstlen)