linux-kernel - Re: [PATCH v2 4/9] remoteproc: mediatek: Support probing for the 2nd core of dual-core SCP

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Message-ID: <20220829194247.GC2264818@p14s>
Date:   Mon, 29 Aug 2022 13:42:47 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Tinghan Shen <tinghan.shen@...iatek.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Lee Jones <lee.jones@...aro.org>,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Daisuke Nojiri <dnojiri@...omium.org>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Prashant Malani <pmalani@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        chrome-platform@...ts.linux.dev,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        weishunc@...gle.com
Subject: Re: [PATCH v2 4/9] remoteproc: mediatek: Support probing for the 2nd
 core of dual-core SCP

On Wed, Jun 08, 2022 at 04:35:48PM +0800, Tinghan Shen wrote:
> The mtk_scp.c driver only supports the single core SCP and the
> 1st core of a dual-core SCP. This patch extends it for the 2nd core.
> 
> MT8195 SCP is a dual-core MCU. Both cores are housed in the same subsys.

s/subsys/subsystem

> They have the same viewpoint of registers and memory.
> 
> Core 1 of the SCP features its own set of core configuration registers,
> interrupt controller, timers, and DMAs. The rest of the peripherals
> in this subsystem are shared by core 0 and core 1.
> 
> As for memory, core 1 has its own cache memory. the SCP SRAM is shared

/the/The

> by core 0 and core 1.
> 
> Signed-off-by: Tinghan Shen <tinghan.shen@...iatek.com>
> ---
>  drivers/remoteproc/mtk_scp.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
> index 3510c6d0bbc8..91b4aefde4ac 100644
> --- a/drivers/remoteproc/mtk_scp.c
> +++ b/drivers/remoteproc/mtk_scp.c
> @@ -23,6 +23,10 @@
>  #define MAX_CODE_SIZE 0x500000
>  #define SECTION_NAME_IPI_BUFFER ".ipi_buffer"
>  
> +#define SCP_CORE_0 0
> +#define SCP_CORE_1 1
> +#define SCP_CORE_SINGLE 0xF
> +
>  /**
>   * scp_get() - get a reference to SCP.
>   *
> @@ -836,6 +840,7 @@ static int scp_probe(struct platform_device *pdev)
>  	struct resource *res;
>  	const char *fw_name = "scp.img";
>  	int ret, i;
> +	u32 core_id = SCP_CORE_SINGLE;
>  
>  	ret = rproc_of_parse_firmware(dev, 0, &fw_name);
>  	if (ret < 0 && ret != -EINVAL)
> @@ -851,8 +856,16 @@ static int scp_probe(struct platform_device *pdev)
>  	scp->data = of_device_get_match_data(dev);
>  	platform_set_drvdata(pdev, scp);
>  
> +	ret = of_property_read_u32_index(dev->of_node, "mediatek,scp-core", 1, &core_id);
> +	if (ret == 0)
> +		dev_info(dev, "Boot SCP dual core %u\n", core_id);

Why is the DT property "mediatek,scp-core" needed at all?  Since the compatible
"mediatek,mt8195-scp-dual" has already been defined previously in this patchset,
initialising the second core, if present, is a matter of looking at the
compatile string. 

> +
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "sram");
> -	scp->sram_base = devm_ioremap_resource(dev, res);
> +	if (core_id == SCP_CORE_1)
> +		scp->sram_base = devm_ioremap(dev, res->start, resource_size(res));
> +	else
> +		scp->sram_base = devm_ioremap_resource(dev, res);
> +

This looks very broken...  For this to work you would need to have two DT
entries with the "mediatek,mt8195-scp-dual" compatible properly, one with
"mediatek,scp-core = <&scp_dual1 0>;" and another one with "mediatek,scp-core = <&scp_dual0 1>;".

Which is also very broken...  Here you have a binding whose first argument is a
reference to the core sibling while the second argument is a characteristic of
the current core, which is highly confusing.

I suggest what when you see the compatible binding "mediatek,mt8195-scp", a
single core is initialized.  If you see "mediatek,mt8195-scp-dual", both cores
are initialized as part of the _same_ probe.

If the above analysis is not correct it means I misinterpreted your
work and if so, a serious amount of comments is needed _and_ a very detailed
example in "mtk,scp.yaml" that leaves no room for interpretation.

I will stop reviewing this patchset until you have clarified how this works.

Thanks,
Mathieu

>  	if (IS_ERR(scp->sram_base))
>  		return dev_err_probe(dev, PTR_ERR(scp->sram_base),
>  				     "Failed to parse and map sram memory\n");
> @@ -873,7 +886,12 @@ static int scp_probe(struct platform_device *pdev)
>  		scp->l1tcm_phys = res->start;
>  	}
>  
> -	scp->reg_base = devm_platform_ioremap_resource_byname(pdev, "cfg");
> +	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "cfg");
> +	if (core_id == SCP_CORE_1)
> +		scp->reg_base = devm_ioremap(dev, res->start, resource_size(res));
> +	else
> +		scp->reg_base = devm_ioremap_resource(dev, res);
> +
>  	if (IS_ERR(scp->reg_base))
>  		return dev_err_probe(dev, PTR_ERR(scp->reg_base),
>  				     "Failed to parse and map cfg memory\n");
> -- 
> 2.18.0
>