[PATCH v2 3/4] arm64: dts: qcom: sc7180: Mark SCM as dma-coherent for trogdor

[Douglas Anderson]

Trogdor devices use firmware backed by TF-A instead of Qualcomm's
normal TZ. On TF-A we end up mapping memory as cacheable.
Specifically, you can see in Trogdor's TF-A code [1] in
qti_sip_mem_assign() that we call qti_mmap_add_dynamic_region() with
MT_RO_DATA. This translates down to MT_MEMORY instead of
MT_NON_CACHEABLE or MT_DEVICE. Apparently Qualcomm's normal TZ
implementation maps the memory as non-cacheable.

Let's add the "dma-coherent" attribute to the SCM for trogdor.

Adding "dma-coherent" like this fixes WiFi on sc7180-trogdor
devices. WiFi was broken as of commit 7bd6680b47fa ("Revert "Revert
"arm64: dma: Drop cache invalidation from
arch_dma_prep_coherent()"""). Specifically at bootup we'd get:

 qcom_scm firmware:scm: Assign memory protection call failed -22
 qcom_rmtfs_mem 94600000.memory: assign memory failed
 qcom_rmtfs_mem: probe of 94600000.memory failed with error -22

>From discussion on the mailing lists [2] and over IRC [3], it was
determined that we should always have been tagging the SCM as
dma-coherent on trogdor but that the old "invalidate" happened to make
things work most of the time. Tagging it properly like this is a much
more robust solution.

[1] https://chromium.googlesource.com/chromiumos/third_party/arm-trusted-firmware/+/refs/heads/firmware-trogdor-13577.B/plat/qti/common/src/qti_syscall.c
[2] https://lore.kernel.org/r/20230614165904.1.I279773c37e2c1ed8fbb622ca6d1397aea0023526@changeid
[3] https://oftc.irclog.whitequark.org/linux-msm/2023-06-15

Fixes: 7bd6680b47fa ("Revert "Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()""")
Fixes: 7ec3e67307f8 ("arm64: dts: qcom: sc7180-trogdor: add initial trogdor and lazor dt")
Reviewed-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxx>
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

Changes in v2:
- Add comment in dts.
- Moved scm node out of pinctrl section to the proper place.

 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
index ca6920de7ea8..1472e7f10831 100644
--- a/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
+++ b/arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
@@ -892,6 +892,11 @@ &remoteproc_mpss {
 	qcom,spare-regs = <&tcsr_regs_2 0xb3e4>;
 };
 
+&scm {
+	/* TF-A firmware maps memory cached so mark dma-coherent to match. */
+	dma-coherent;
+};
+
 &sdhc_1 {
 	status = "okay";
 
-- 
2.41.0.162.gfafddb0af9-goog