linux-kernel - Re: [PATCH v3 8/8] memory: gpmc-omap: "gpmc,device-width" DT property is optional

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Date:   Wed, 15 Sep 2021 12:11:04 +0300
From:   Roger Quadros <rogerq@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        tony@...mide.com
Cc:     robh+dt@...nel.org, grygorii.strashko@...com, nm@...com,
        lokeshvutla@...com, nsekhar@...com, miquel.raynal@...tlin.com,
        devicetree@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 8/8] memory: gpmc-omap: "gpmc,device-width" DT property
 is optional

Hi Krzysztof,

On 07/09/2021 15:36, Krzysztof Kozlowski wrote:
> On 07/09/2021 13:32, Roger Quadros wrote:
>> Check for valid gpmc,device-width, nand-bus-width and bank-width
>> at one place. Default to 8-bit width if none present.
> 
> I don't understand the message in the context of the patch. The title
> says one property is optional - that's it. The message says you
> consolidate checks. How is this related to the title?
> 
> The patch itself moves around checking of properties and reads
> nand-bus-width *always*. It does not "check at one place" but rather
> "check always". In the same time, the patch does not remove
> gpmc,device-width check in other place.
> 
> All three elements - the title, message and patch - do different things.
> What did you want to achieve here? Can you help in clarifying it?
> 

OK I will explain it better in commit log in next revision. Let me explain here a bit.

Prior to this patch it was working like this

	/* in gpmc_read_settings_dt() */
	s->device_width = 0;	/* invalid width, should be 1 for 8-bit, 2 for 16-bit */
	of_property_read_u32(np, "gpmc,device-width", s->device_width);

	/* in gpmc_probe_generic_child () */
	if (of_device_is_compatible(child, "ti,omap2-nand")) {
		/* check for nand-bus-width, if absent set s->device_width to 1 (i.e. 8-bit) */
	} else {
		/* check for bank-width, if absent and s->device_width not set, error out */
	}

So that means if all three, "gpmc,device-width". "nand-bus-width" and "bank-width" are missing then
it would create an error situation.

The patch is doing 3 things.
1) Make sure all DT checks related to bus width are being done at one place for better readability.
2) even if all 3 width properties are absent, we will not treat it as error and default to 8-bit.
3) check for nand-bus-width regardless of whether compatible to "ti,omap2-nand" or not.

Hope this explains well.

cheers,
-roger

> 
> Best regards,
> Krzysztof
> 
> 
>>
>> Signed-off-by: Roger Quadros <rogerq@...nel.org>
>> ---
>>  drivers/memory/omap-gpmc.c | 41 ++++++++++++++++++++++++--------------
>>  1 file changed, 26 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/memory/omap-gpmc.c b/drivers/memory/omap-gpmc.c
>> index f80c2ea39ca4..32d7c665f33c 100644
>> --- a/drivers/memory/omap-gpmc.c
>> +++ b/drivers/memory/omap-gpmc.c
>> @@ -2171,10 +2171,8 @@ static int gpmc_probe_generic_child(struct platform_device *pdev,
>>  		}
>>  	}
>>  
>> -	if (of_device_is_compatible(child, "ti,omap2-nand")) {
>> -		/* NAND specific setup */
>> -		val = 8;
>> -		of_property_read_u32(child, "nand-bus-width", &val);
>> +	/* DT node can have "nand-bus-width" or "bank-width" or "gpmc,device-width" */
>> +	if (!of_property_read_u32(child, "nand-bus-width", &val)) {
>>  		switch (val) {
>>  		case 8:
>>  			gpmc_s.device_width = GPMC_DEVWIDTH_8BIT;
>> @@ -2183,24 +2181,37 @@ static int gpmc_probe_generic_child(struct platform_device *pdev,
>>  			gpmc_s.device_width = GPMC_DEVWIDTH_16BIT;
>>  			break;
>>  		default:
>> -			dev_err(&pdev->dev, "%pOFn: invalid 'nand-bus-width'\n",
>> -				child);
>> +			dev_err(&pdev->dev,
>> +				"%pOFn: invalid 'nand-bus-width':%d\n", child, val);
>> +			ret = -EINVAL;
>> +			goto err;
>> +		}
>> +	} else if (!of_property_read_u32(child, "bank-width", &val)) {
>> +		if (val != 1 && val != 2) {
>> +			dev_err(&pdev->dev,
>> +				"%pOFn: invalid 'bank-width':%d\n", child, val);
>>  			ret = -EINVAL;
>>  			goto err;
>>  		}
>> +		gpmc_s.device_width = val;
>> +	} else if (!of_property_read_u32(child, "gpmc,device-width", &val)) {
>> +		if (val != 1 && val != 2) {
>> +			dev_err(&pdev->dev,
>> +				"%pOFn: invalid 'gpmc,device-width':%d\n", child, val);
>> +			ret = -EINVAL;
>> +			goto err;
>> +		}
>> +		gpmc_s.device_width = val;
>> +	} else {
>> +		/* default to 8-bit */
>> +		gpmc_s.device_width = GPMC_DEVWIDTH_8BIT;
>> +	}
>>  
>> +	if (of_device_is_compatible(child, "ti,omap2-nand")) {
>> +		/* NAND specific setup */
>>  		/* disable write protect */
>>  		gpmc_configure(GPMC_CONFIG_WP, 0);
>>  		gpmc_s.device_nand = true;
>> -	} else {
>> -		ret = of_property_read_u32(child, "bank-width",
>> -					   &gpmc_s.device_width);
>> -		if (ret < 0 && !gpmc_s.device_width) {
>> -			dev_err(&pdev->dev,
>> -				"%pOF has no 'gpmc,device-width' property\n",
>> -				child);
>> -			goto err;
>> -		}
>>  	}
>>  
>>  	/* Reserve wait pin if it is required and valid */
>>
> 
>