Re: [PATCH v10 13/15] firmware: qcom: scm: clarify the comment in qcom_scm_pas_init_image()

[Elliot Berman <quic_eberman@quicinc.com>]

On Mon, May 27, 2024 at 02:55:03PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@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@linaro.org>
> Tested-by: Andrew Halaney <ahalaney@redhat.com> # sc8280xp-lenovo-thinkpad-x13s
> Tested-by: Deepti Jaggi <quic_djaggi@quicinc.com> #sa8775p-ride
> Reviewed-by: Elliot Berman <quic_eberman@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 c82957727650..86e26f17ca19 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -583,6 +583,13 @@ 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
                                Linux
> +	 * 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);
> 
> -- 
> 2.43.0
>