misc: fastrpc: use coherent pool for untranslated Compute Banks

Use fastrpc_remote_heap_alloc to allocate from the FastRPC device
instead of the Compute Bank when the session ID is 0. This ensures
that the allocation is inside the coherent DMA pool which is already
accessible to the DSP. This is necessary to support FastRPC devices
which do not have dedicated Compute Banks such as the SLPI on the SDM845.
The latter uses an allocated CMA region instead of FastRPC Compute Banks.
Signed-off-by: Dylan Van Assche <me@dylanvanassche.be>
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Ekansh Gupta <quic_ekangupt@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20240705075900.424100-6-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -953,7 +953,10 @@ static int fastrpc_get_args(u32 kernel, struct fastrpc_invoke_ctx *ctx)
 
 	ctx->msg_sz = pkt_size;
 
-	err = fastrpc_buf_alloc(ctx->fl, dev, pkt_size, &ctx->buf);
+	if (ctx->fl->sctx->sid)
+		err = fastrpc_buf_alloc(ctx->fl, dev, pkt_size, &ctx->buf);
+	else
+		err = fastrpc_remote_heap_alloc(ctx->fl, dev, pkt_size, &ctx->buf);
 	if (err)
 		return err;