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

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Date:	Sun, 7 Jun 2015 15:32:02 -0000
From:	ygardi@...eaurora.org
To:	"Akinobu Mita" <akinobu.mita@...il.com>
Cc:	"Yaniv Gardi" <ygardi@...eaurora.org>, 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.
>

again, Mita, your comments are very appreciated.

1)
If ufshcd-pltfrm driver is loaded before ufs-qcom, (what actually happens
always), then the calling to of_platform_populate() which is added,
guarantees that ufs-qcom probe will be called and finish, before
ufshcd_pltfrm probe continues.
so ufs_variant device is always there, and ready.
I think it means we are safe - since either way, we make sure ufs-qcom
probe will be called and finish before dealing with ufs_variant device in
ufshcd_pltfrm probe.

2) you are right. the fix added as you suggested.

let us know your thoughts about the V3 once it's uploaded

thanks



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