[PATCH v8 11/12] firmware: qcom: scm: clarify the comment in qcom_scm_pas_init_image()

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bartosz.golaszewski at linaro.org>

The "memory protection" mechanism mentioned in the comment is the SHM
Bridge. This is also the reason why we do not convert this call to using
the TZ memory allocator.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski at linaro.org>
Tested-by: Andrew Halaney <ahalaney at redhat.com> # sc8280xp-lenovo-thinkpad-x13s
Tested-by: Deepti Jaggi <quic_djaggi at quicinc.com> #sa8775p-ride
Reviewed-by: Elliot Berman <quic_eberman at quicinc.com>
---
 drivers/firmware/qcom/qcom_scm.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index 811f93edac7f..fbacc959b6fa 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -566,6 +566,13 @@ int qcom_scm_pas_init_image(u32 peripheral, const void *metadata, size_t size,
 	 * During the scm call memory protection will be enabled for the meta
 	 * data blob, so make sure it's physically contiguous, 4K aligned and
 	 * non-cachable to avoid XPU violations.
+	 *
+	 * For PIL calls the hypervisor creates SHM Bridges for the blob
+	 * buffers on behalf of Linus so we must not do it ourselves hence
+	 * not using the TZMem allocator here.
+	 *
+	 * If we pass a buffer that is already part of an SHM Bridge to this
+	 * call, it will fail.
 	 */
 	mdata_buf = dma_alloc_coherent(__scm->dev, size, &mdata_phys,
 				       GFP_KERNEL);
-- 
2.40.1