linux-kernel - Re: [PATCH v4 2/2] net: qcom/emac: Find sgmii_ops by device_for_each

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Message-ID: <1f5d984b-4182-4350-a4b6-a3c42bad88e6@quicinc.com>
Date: Thu, 5 Sep 2024 16:29:56 +0800
From: quic_zijuhu <quic_zijuhu@...cinc.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Zijun Hu
	<zijun_hu@...oud.com>
CC: Davidlohr Bueso <dave@...olabs.net>,
        Jonathan Cameron
	<jonathan.cameron@...wei.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alison
 Schofield <alison.schofield@...el.com>,
        Vishal Verma
	<vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Dan Williams
	<dan.j.williams@...el.com>,
        Timur Tabi <timur@...nel.org>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, <linux-cxl@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] net: qcom/emac: Find sgmii_ops by
 device_for_each_child()

On 9/5/2024 1:29 PM, Greg Kroah-Hartman wrote:
> On Thu, Sep 05, 2024 at 08:36:10AM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@...cinc.com>
>>
>> To prepare for constifying the following old driver core API:
>>
>> struct device *device_find_child(struct device *dev, void *data,
>> 		int (*match)(struct device *dev, void *data));
>> to new:
>> struct device *device_find_child(struct device *dev, const void *data,
>> 		int (*match)(struct device *dev, const void *data));
>>
>> The new API does not allow its match function (*match)() to modify
>> caller's match data @*data, but emac_sgmii_acpi_match() as the old
>> API's match function indeed modifies relevant match data, so it is not
>> suitable for the new API any more, solved by using device_for_each_child()
>> to implement relevant finding sgmii_ops function.
>>
>> By the way, this commit does not change any existing logic.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>>  drivers/net/ethernet/qualcomm/emac/emac-sgmii.c | 22 +++++++++++++++++-----
>>  1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/qualcomm/emac/emac-sgmii.c b/drivers/net/ethernet/qualcomm/emac/emac-sgmii.c
>> index e4bc18009d08..29392c63d115 100644
>> --- a/drivers/net/ethernet/qualcomm/emac/emac-sgmii.c
>> +++ b/drivers/net/ethernet/qualcomm/emac/emac-sgmii.c
>> @@ -293,6 +293,11 @@ static struct sgmii_ops qdf2400_ops = {
>>  };
>>  #endif
>>  
>> +struct emac_match_data {
>> +	struct sgmii_ops **sgmii_ops;
>> +	struct device *target_device;
>> +};
>> +
>>  static int emac_sgmii_acpi_match(struct device *dev, void *data)
>>  {
>>  #ifdef CONFIG_ACPI
>> @@ -303,7 +308,7 @@ static int emac_sgmii_acpi_match(struct device *dev, void *data)
>>  		{}
>>  	};
>>  	const struct acpi_device_id *id = acpi_match_device(match_table, dev);
>> -	struct sgmii_ops **ops = data;
>> +	struct emac_match_data *match_data = data;
>>  
>>  	if (id) {
>>  		acpi_handle handle = ACPI_HANDLE(dev);
>> @@ -324,10 +329,12 @@ static int emac_sgmii_acpi_match(struct device *dev, void *data)
>>  
>>  		switch (hrv) {
>>  		case 1:
>> -			*ops = &qdf2432_ops;
>> +			*match_data->sgmii_ops = &qdf2432_ops;
>> +			match_data->target_device = get_device(dev);
>>  			return 1;
>>  		case 2:
>> -			*ops = &qdf2400_ops;
>> +			*match_data->sgmii_ops = &qdf2400_ops;
>> +			match_data->target_device = get_device(dev);
> 
> Where is put_device() now called?
> 
>>  			return 1;
>>  		}
>>  	}
>> @@ -356,10 +363,15 @@ int emac_sgmii_config(struct platform_device *pdev, struct emac_adapter *adpt)
>>  	int ret;
>>  
>>  	if (has_acpi_companion(&pdev->dev)) {
>> +		struct emac_match_data match_data = {
>> +			.sgmii_ops = &phy->sgmii_ops,
>> +			.target_device = NULL,
>> +		};
>>  		struct device *dev;
>>  
>> -		dev = device_find_child(&pdev->dev, &phy->sgmii_ops,
>> -					emac_sgmii_acpi_match);
>> +		device_for_each_child(&pdev->dev, &match_data, emac_sgmii_acpi_match);
>> +		/* Need to put_device(@dev) after use */
>> +		dev = match_data.target_device;
> 
> 
> Why this new comment?  That's always required and happens down below in
> the function, right?  Otherwise, what changed?
> 

device_find_child() will get_device() by itself and that is obvious.

device_for_each_child() will not get_device() by itself, we get_device()
in its function parameter to make it equivalent with device_find_child()
this get_device() is not obvious, so add the inline comments to prompt
user put_device after use.

yes, and the relevant put_device() don't happen immediately.

> thanks,
> 
> greg k-h