On Tue, May 30, 2023 at 04:36:42PM -0700, Bjorn Andersson wrote:
> In some configurations, the exact placement of the rmtfs shared memory
> region isn't so strict. The DeviceTree author can then choose to use the
> "size" property and rely on the OS for placement (in combination with
> "alloc-ranges", if desired).
>
> But on some platforms the rmtfs memory region may not be allocated
> adjacent to regions allocated by other clients. Add support for
> discarding the first and last 4k block in the region, if
> qcom,use-guard-pages is specified in DeviceTree.
>
> Signed-off-by: Bjorn Andersson <quic_bjorande@xxxxxxxxxxx>
> ---
>
> Changes since v1:
> - Drop the dma_alloc_coherent() based approach and just add support for
> the guard pages.
>
> drivers/soc/qcom/rmtfs_mem.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/soc/qcom/rmtfs_mem.c b/drivers/soc/qcom/rmtfs_mem.c
> index f83811f51175..28238974d913 100644
> --- a/drivers/soc/qcom/rmtfs_mem.c
> +++ b/drivers/soc/qcom/rmtfs_mem.c
> @@ -213,6 +213,16 @@ static int qcom_rmtfs_mem_probe(struct platform_device *pdev)
> goto put_device;
> }
>
> + /*
> + * If requested, discard the first and last 4k block in order to ensure
> + * that the rmtfs region isn't adjacent to other protected regions.
> + */
> + if (of_property_present(node, "qcom,use-guard-pages")) {
> + rmtfs_mem->addr += SZ_4K;
> + rmtfs_mem->base += SZ_4K;
> + rmtfs_mem->size -= 2 * SZ_4K;
> + }
It probably doesn't make a big difference in practice but I would say
there is no need to even memremap() the guard pages. If you adjust the
->addr and ->size before the memremap() then you don't need to modify
the ->base at all.
Thanks,
Stephan
