linux-kernel - Re: [PATCH] phy: ti: gmii-sel: Allow parent to not be syscon node

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Date:   Mon, 10 Jul 2023 09:38:11 -0500
From:   Andrew Davis <afd@...com>
To:     Siddharth Vadapalli <s-vadapalli@...com>
CC:     Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Roger Quadros <rogerq@...nel.org>,
        <linux-phy@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] phy: ti: gmii-sel: Allow parent to not be syscon node

On 5/15/23 11:05 PM, Siddharth Vadapalli wrote:
> Andrew,
> 
> On 16/05/23 01:29, Andrew Davis wrote:
>> If the parent node is not a syscon type, then fallback and check
>> if we can get a regmap from our own node. This no longer forces
>> us to make the parent of this node a syscon node when that might
>> not be appropriate.
> 
> Could you please let me know in which cases it is appropriate versus in which
> cases it isn't?

Use of syscon nodes should be discouraged, in most cases they can and should be
avoided. The only time we would need to have a syscon parent is when the register
space contains multiple sub-devices with bit level interleaving.

Most devices should never need syscon, we overuse syscon due to driver like
this that have no other option than to make the parent device a syscon node.

> Is syscon_node_to_regmap() being retained for backward
> compatibility until the device-tree nodes are cleaned up across all devices?
> 

Yes, the old way is left only for backwards compatibility.

>>
>> Signed-off-by: Andrew Davis <afd@...com>
>> ---
>>   drivers/phy/ti/phy-gmii-sel.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/phy/ti/phy-gmii-sel.c b/drivers/phy/ti/phy-gmii-sel.c
>> index 8c667819c39a..1e67ed9a5cf6 100644
>> --- a/drivers/phy/ti/phy-gmii-sel.c
>> +++ b/drivers/phy/ti/phy-gmii-sel.c
>> @@ -435,9 +435,12 @@ static int phy_gmii_sel_probe(struct platform_device *pdev)
>>   
>>   	priv->regmap = syscon_node_to_regmap(node->parent);
>>   	if (IS_ERR(priv->regmap)) {
>> -		ret = PTR_ERR(priv->regmap);
>> -		dev_err(dev, "Failed to get syscon %d\n", ret);
>> -		return ret;
>> +		priv->regmap = device_node_to_regmap(node);
> 
> If device_node_to_regmap() can always be used with the corresponding changes
> made to the device-tree nodes, wouldn't it be better to use it directly instead
> of using it as a fallback? (This is based on the assumption that
> syscon_node_to_regmap() is only being retained until the device-tree nodes are
> cleaned up to work with device_node_to_regmap()).
> 

Yes, that could work too. I was trying to make the minimal changes here, but
if we feel it works better we can have the default be to check the self node first.

Andrew

>> +		if (IS_ERR(priv->regmap)) {
>> +			ret = PTR_ERR(priv->regmap);
>> +			dev_err(dev, "Failed to get syscon %d\n", ret);
>> +			return ret;
>> +		}
>>   	}
>>   
>>   	ret = phy_gmii_sel_init_ports(priv);
>