linux-kernel - Re: [PATCH 1/2] PCI: dwc: dra7xx: Use syscon_regmap_lookup_by_phandle

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Message-ID: <20250115230430.GA560547@bhelgaas>
Date: Wed, 15 Jan 2025 17:04:30 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Vignesh Raghavendra <vigneshr@...com>,
	Siddharth Vadapalli <s-vadapalli@...com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Minghuan Lian <minghuan.Lian@....com>,
	Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>,
	linux-omap@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, imx@...ts.linux.dev
Subject: Re: [PATCH 1/2] PCI: dwc: dra7xx: Use
 syscon_regmap_lookup_by_phandle_args

On Sun, Jan 12, 2025 at 02:39:02PM +0100, Krzysztof Kozlowski wrote:
> Use syscon_regmap_lookup_by_phandle_args() which is a wrapper over
> syscon_regmap_lookup_by_phandle() combined with getting the syscon
> argument.  Except simpler code this annotates within one line that given
> phandle has arguments, so grepping for code would be easier.
> 
> There is also no real benefit in printing errors on missing syscon
> argument, because this is done just too late: runtime check on
> static/build-time data.  Dtschema and Devicetree bindings offer the
> static/build-time check for this already.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---
>  drivers/pci/controller/dwc/pci-dra7xx.c | 27 ++++++---------------------
>  1 file changed, 6 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
> index 5c62e1a3ba52919afe96fbcbc6edaf70775a69cb..33d6bf460ffe5bb724a061558dd93ec7bdadc336 100644
> --- a/drivers/pci/controller/dwc/pci-dra7xx.c
> +++ b/drivers/pci/controller/dwc/pci-dra7xx.c
> @@ -635,30 +635,20 @@ static int dra7xx_pcie_unaligned_memaccess(struct device *dev)
>  {
>  	int ret;
>  	struct device_node *np = dev->of_node;
> -	struct of_phandle_args args;
> +	unsigned int args[2];
>  	struct regmap *regmap;
>  
> -	regmap = syscon_regmap_lookup_by_phandle(np,
> -						 "ti,syscon-unaligned-access");
> +	regmap = syscon_regmap_lookup_by_phandle_args(np, "ti,syscon-unaligned-access",
> +						      2, args);
>  	if (IS_ERR(regmap)) {
>  		dev_dbg(dev, "can't get ti,syscon-unaligned-access\n");
>  		return -EINVAL;
>  	}
>  
> -	ret = of_parse_phandle_with_fixed_args(np, "ti,syscon-unaligned-access",
> -					       2, 0, &args);
> -	if (ret) {
> -		dev_err(dev, "failed to parse ti,syscon-unaligned-access\n");
> -		return ret;
> -	}
> -
> -	ret = regmap_update_bits(regmap, args.args[0], args.args[1],
> -				 args.args[1]);
> +	ret = regmap_update_bits(regmap, args[0], args[1], args[1]);
>  	if (ret)
>  		dev_err(dev, "failed to enable unaligned access\n");
>  
> -	of_node_put(args.np);
> -
>  	return ret;
>  }
>  
> @@ -671,18 +661,13 @@ static int dra7xx_pcie_configure_two_lane(struct device *dev,
>  	u32 mask;
>  	u32 val;
>  
> -	pcie_syscon = syscon_regmap_lookup_by_phandle(np, "ti,syscon-lane-sel");
> +	pcie_syscon = syscon_regmap_lookup_by_phandle_args(np, "ti,syscon-lane-sel",
> +							   1, &pcie_reg);
>  	if (IS_ERR(pcie_syscon)) {
>  		dev_err(dev, "unable to get ti,syscon-lane-sel\n");
>  		return -EINVAL;
>  	}
>  
> -	if (of_property_read_u32_index(np, "ti,syscon-lane-sel", 1,
> -				       &pcie_reg)) {
> -		dev_err(dev, "couldn't get lane selection reg offset\n");
> -		return -EINVAL;
> -	}

Wow.  I believe you that syscon_regmap_lookup_by_phandle_args() is
equivalent to both:

  - syscon_regmap_lookup_by_phandle() followed by
    of_parse_phandle_with_fixed_args(), and

  - syscon_regmap_lookup_by_phandle() followed by
    of_property_read_u32_index()

but I can't say it's obvious to this syscon- and OF-naive reviewer,
even after tracing a few layers in :)

Bjorn