linux-kernel - Re: [PATCH v2 05/10] soc: sunxi: sram: Fix probe function ordering issues

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Date:   Mon, 15 Aug 2022 19:05:12 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Heiko Stübner <heiko@...ech.de>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Hans de Goede <hdegoede@...hat.com>,
        Icenowy Zheng <icenowy@...c.io>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maxime Ripard <mripard@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH v2 05/10] soc: sunxi: sram: Fix probe function ordering
 issues

On 8/15/22 9:06 AM, Heiko Stübner wrote:
> Am Montag, 15. August 2022, 06:12:42 CEST schrieb Samuel Holland:
>> Errors from debugfs are intended to be non-fatal, and should not prevent
>> the driver from probing.
>>
>> Since debugfs file creation is treated as infallible, move it below the
>> parts of the probe function that can fail. This prevents an error
>> elsewhere in the probe function from causing the file to leak. Do the
>> same for the call to of_platform_populate().
>>
>> Finally, checkpatch suggests an octal literal for the file permissions.
>>
>> Fixes: 4af34b572a85 ("drivers: soc: sunxi: Introduce SoC driver to map SRAMs")
>> Fixes: 5828729bebbb ("soc: sunxi: export a regmap for EMAC clock reg on A64")
>> Reviewed-by: Jernej Skrabec <jernej.skrabec@...il.com>
>> Signed-off-by: Samuel Holland <samuel@...lland.org>
> 
> Tested-by: Heiko Stuebner <heiko@...ech.de>
> 
> but one thing below
> 
>> ---
>>
>> (no changes since v1)
>>
>>  drivers/soc/sunxi/sunxi_sram.c | 13 +++++--------
>>  1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/soc/sunxi/sunxi_sram.c b/drivers/soc/sunxi/sunxi_sram.c
>> index a858a37fcdd4..52d07bed7664 100644
>> --- a/drivers/soc/sunxi/sunxi_sram.c
>> +++ b/drivers/soc/sunxi/sunxi_sram.c
>> @@ -332,9 +332,9 @@ static struct regmap_config sunxi_sram_emac_clock_regmap = {
>>  
>>  static int __init sunxi_sram_probe(struct platform_device *pdev)
>>  {
>> -	struct dentry *d;
>>  	struct regmap *emac_clock;
>>  	const struct sunxi_sramc_variant *variant;
>> +	struct device *dev = &pdev->dev;
>>  
>>  	sram_dev = &pdev->dev;
>>  
>> @@ -346,13 +346,6 @@ static int __init sunxi_sram_probe(struct platform_device *pdev)
>>  	if (IS_ERR(base))
>>  		return PTR_ERR(base);
>>  
>> -	of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);
>> -
>> -	d = debugfs_create_file("sram", S_IRUGO, NULL, NULL,
>> -				&sunxi_sram_fops);
>> -	if (!d)
>> -		return -ENOMEM;
>> -
>>  	if (variant->num_emac_clocks > 0) {
>>  		emac_clock = devm_regmap_init_mmio(&pdev->dev, base,
>>  						   &sunxi_sram_emac_clock_regmap);
>> @@ -361,6 +354,10 @@ static int __init sunxi_sram_probe(struct platform_device *pdev)
>>  			return PTR_ERR(emac_clock);
>>  	}
>>  
>> +	of_platform_populate(dev->of_node, NULL, NULL, dev);
> 
> hmm, of_platform_populate() can actually fail [0] it just looks a bit like
> sunxi driver seem to ignore that by {chance, design?} [1] .
> 
> So I guess this might want to have handling for probably unlikely
> possible errors instead?

Strictly speaking, neither this driver nor the DE2 bus driver depend on any of
the child nodes having a platform device present or a driver attached. So
failing to populate the child devices should not necessarily prevent this driver
from probing. Possibly it deserves a dev_warn(), but...

I don't think of_platform_populate() can actually fail when passed a valid node.
of_platform_bus_create() calls itself recursively, but otherwise always returns 0.

Regards,
Samuel

> Heiko
> 
> [0] https://elixir.bootlin.com/linux/latest/source/drivers/of/platform.c#L463
> [1] https://elixir.bootlin.com/linux/latest/source/drivers/bus/sun50i-de2.c#L22
>> +
>> +	debugfs_create_file("sram", 0444, NULL, NULL, &sunxi_sram_fops);
>> +
>>  	return 0;
>>  }