linux-kernel - Re: [PATCH v3 2/3] soc: qcom: rmtfs: Support discarding guard pages

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Date:   Thu, 21 Sep 2023 20:04:06 +0200
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] soc: qcom: rmtfs: Support discarding guard pages

On Wed, Sep 20, 2023 at 07:37:31PM -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@...cinc.com>
> ---
>  drivers/soc/qcom/rmtfs_mem.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/soc/qcom/rmtfs_mem.c b/drivers/soc/qcom/rmtfs_mem.c
> index f83811f51175..83bba9321e72 100644
> --- a/drivers/soc/qcom/rmtfs_mem.c
> +++ b/drivers/soc/qcom/rmtfs_mem.c
> @@ -200,6 +200,15 @@ static int qcom_rmtfs_mem_probe(struct platform_device *pdev)
>  	rmtfs_mem->client_id = client_id;
>  	rmtfs_mem->size = rmem->size;
>  
> +	/*
> +	 * 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")) {

I think of_property_read_bool() would be more fitting here. Right now
of_property_present() is just a wrapper around of_property_read_bool().
Semantically reading a bool fits better here though. :-)

Feel free to fix that up while applying.

FWIW I don't really have an opinion if "qcom,use-guard-pages" is a good
way to describe this in the DT. For the implementation side feel free to
add my

Reviewed-by: Stephan Gerhold <stephan@...hold.net>

Thanks,
Stephan

> +		rmtfs_mem->addr += SZ_4K;
> +		rmtfs_mem->size -= 2 * SZ_4K;
> +	}
> +
>  	device_initialize(&rmtfs_mem->dev);
>  	rmtfs_mem->dev.parent = &pdev->dev;
>  	rmtfs_mem->dev.groups = qcom_rmtfs_mem_groups;
> 
> -- 
> 2.25.1
>