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

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Date:	Sat, 6 Jun 2015 01:47:45 +0900
From:	Akinobu Mita <akinobu.mita@...il.com>
To:	Yaniv Gardi <ygardi@...eaurora.org>
Cc:	merez@....qualcomm.com, dovl@....qualcomm.com,
	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

2015-06-05 5:53 GMT+09:00  <ygardi@...eaurora.org>:
>> 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 explanation, I agree with it.

I found two problems in the current code, but both can be fixed
relatively easily as described below:

1) If ufshcd-pltfrm driver is loaded before ufs-qcom driver,
ufshcd_pltfrm_probe() can't find a ufs_variant device.

In order to trigger re-probing ufs device when ufs-qcom driver has
been loaded, ufshcd_pltfrm_probe() should return -EPROBE_DEFER in
case 'ufs_variant' sub-node exists and no hba->vops found.

2) Nothing prevents ufs-qcom module from being unloaded while the
variant_ops is referenced by ufshcd-pltfrm.

It can be fixed by incrementing module refcount of ufs_variant module
by __module_get(ufs_variant_pdev->dev.driver->owener) in
ufshcd_pltfrm_probe(), and module_put() in ufshcd_pltfrm_remove()
to descrement the refcount.
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