linux-kernel - Re: [PATCH v2 4/4] scsi: ufs: probe and init of variant driver from the platform device

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Date:	Thu, 4 Jun 2015 20:53:16 -0000
From:	ygardi@...eaurora.org
To:	"Akinobu Mita" <akinobu.mita@...il.com>, merez@....qualcomm.com,
	dovl@....qualcomm.com
Cc:	"Yaniv Gardi" <ygardi@...eaurora.org>,
	"Jej B" <james.bottomley@...senpartnership.com>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org, "Santosh Y" <santoshsy@...il.com>,
	linux-scsi-owner@...r.kernel.org,
	"Subhash Jadavani" <subhashj@...eaurora.org>,
	"Paul Bolle" <pebolle@...cali.nl>,
	"Gilad Broner" <gbroner@...eaurora.org>,
	"Rob Herring" <robh+dt@...nel.org>,
	"Pawel Moll" <pawel.moll@....com>,
	"Mark Rutland" <mark.rutland@....com>,
	"Ian Campbell" <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>,
	"Vinayak Holikatti" <vinholikatti@...il.com>,
	"James E.J. Bottomley" <jbottomley@...n.com>,
	"Dolev Raviv" <draviv@...eaurora.org>,
	"Christoph Hellwig" <hch@....de>,
	"Sujit Reddy Thumma" <sthumma@...eaurora.org>,
	"Raviv Shvili" <rshvili@...eaurora.org>,
	"Sahitya Tummala" <stummala@...eaurora.org>,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] scsi: ufs: probe and init of variant driver from
 the platform device

> Hi Yaniv,
>
> 2015-06-03 18:37 GMT+09:00 Yaniv Gardi <ygardi@...eaurora.org>:
>> @@ -321,7 +313,22 @@ static int ufshcd_pltfrm_probe(struct
>> platform_device *pdev)
>>                 goto out;
>>         }
>>
>> -       hba->vops = get_variant_ops(&pdev->dev);
>> +       err = of_platform_populate(node, NULL, NULL, &pdev->dev);
>> +       if (err)
>> +               dev_err(&pdev->dev,
>> +                       "%s: of_platform_populate() failed\n",
>> __func__);
>> +
>> +       ufs_variant_node = of_get_next_available_child(node, NULL);
>> +
>> +       if (!ufs_variant_node) {
>> +               dev_dbg(&pdev->dev, "failed to find ufs_variant_node
>> child\n");
>> +       } else {
>> +               ufs_variant_pdev =
>> of_find_device_by_node(ufs_variant_node);
>> +
>> +               if (ufs_variant_pdev)
>> +                       hba->vops = (struct ufs_hba_variant_ops *)
>> +                               dev_get_drvdata(&ufs_variant_pdev->dev);
>> +       }
>
> I have no strong objection to 'ufs_variant' sub-node.  But why can't we
> simply add an of_device_id to ufs_of_match, like below:
>
> static const struct of_device_id ufs_of_match[] = {
>         { .compatible = "jedec,ufs-1.1"},
> #if IS_ENABLED(SCSI_UFS_QCOM)
>         { .compatible = "qcom,ufs", .data = &ufs_hba_qcom_vops },
> #neidf
>         {},
> };
>
> and get hba->vops by get_variant_ops()?
>

Hi Mita,
thanks for your comments.

The whole idea, of having a sub-node which includes all variant specific
attributes is to separate the UFS Platform device component, from the need
to know "qcom" or any other future variant.
I believe it keeps the code more modular, and clean - meaning - no
#ifdef's and no need to include all variant attributes inside the driver
DT node.
in that case, we simply have a DT node that is compatible to the Jdec
standard, and sub-node to include variant info.

I hope you agree with this new design, since it provides a good answer
to every future variant that will be added, without the need to change the
platform file.

thanks for your time, Mita
please share your thoughts.

> There is something similar in
> drivers/net/ethernet/freescale/fsl_pq_mdio.c
> --
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