RE: [rtw89] PCI Passthrough Issue: rtl8852be on ARM VM (Ubuntu host/OpenWrt guest)

[Ping-Ke Shih <pkshih@realtek.com>]

lonthn@163.com <lonthn@163.com> wrote:
> Hi rtw89 maintainers,
> I'm having trouble passing through an rtl8852be PCIe device to an ARM KVM guest and hope you could help.
> Key details:
> 
> ==== Environment ====
> * Host: Ubuntu 5.10.160 (ARM)
> * Guest: Openwrt 6.6.73
> * Working case: Identical setup works for rtl8125 passthrough
> 
> ==== Issue ====
> Guest fails to initialize rtl8852be with timeout errors.
> 
> ==== Diagnostic snippets ====

[...]

> [  746.369036] rtw89_8852be 0000:06:00.0: Firmware version 0.29.29.5 (da87cccd), cmd version 0, type 5
> [  746.373384] rtw89_8852be 0000:06:00.0: Firmware version 0.29.29.5 (da87cccd), cmd version 0, type 3
> [  746.377254] rtw89_8852be 0000:06:00.0: [BTC] use version def[6] = 0x001d1d00
> [  747.783549] rtw89_8852be 0000:06:00.0: [ERR]FWDL path ready
> [  747.784119] rtw89_8852be 0000:06:00.0: [ERR]fwdl 0x1E0 = 0x23
> [  747.784652] rtw89_8852be 0000:06:00.0: [ERR]fwdl 0x83F0 = 0x70000

This looks like interoperability problem of 36-bit DMA.
If you have below commit in your guest OS:
1fd4b3fe52ef ("wifi: rtw89: pci: support 36-bit PCI DMA address")

Please also have below commit to rollback 32-bit DMA.
aa70ff0945fe ("wifi: rtw89: pci: early chips only enable 36-bit DMA on specific PCI hosts")

With the latest kernel, you can just comment code as below to use 32-bit DMA.

diff --git a/drivers/net/wireless/realtek/rtw89/pci.c b/drivers/net/wireless/realtek/rtw89/pci.c
index 204a3748d913..3d1a3ac4a1e6 100644
--- a/drivers/net/wireless/realtek/rtw89/pci.c
+++ b/drivers/net/wireless/realtek/rtw89/pci.c
@@ -3141,7 +3141,7 @@ static int rtw89_pci_setup_mapping(struct rtw89_dev *rtwdev,
                goto err;
        }

-       if (!rtw89_pci_is_dac_compatible_bridge(rtwdev))
+       //if (!rtw89_pci_is_dac_compatible_bridge(rtwdev))
                goto try_dac_done;

        ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(36));

> 
> ==== Questions ====
> * Any known ARM passthrough quirks for this chip?

I have not ever tried passthrough, so I'm not sure if it can work.
Can I know how different the passthrough is?

Does rtl8852be work on host OS?

> * Suggested debug steps for error -100?

See my comment above.