linux-kernel - Re: [PATCH] usbip: set the dma mask to 64bit default for vhci-driver

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Message-ID: <b8bc6ce7-55eb-4270-b4dc-d6c853fa65ac@163.com>
Date: Wed, 30 Apr 2025 13:24:31 +0800
From: Zongmin Zhou <min_halo@....com>
To: Shuah Khan <skhan@...uxfoundation.org>,
 Greg KH <gregkh@...uxfoundation.org>
Cc: Christoph Hellwig <hch@...radead.org>, i@...ithal.me,
 linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org, shuah@...nel.org,
 valentina.manea.m@...il.com, Zongmin Zhou <zhouzongmin@...inos.cn>
Subject: Re: [PATCH] usbip: set the dma mask to 64bit default for vhci-driver


On 2025/4/29 07:07, Shuah Khan wrote:
> On 4/28/25 04:04, Greg KH wrote:
>> A: http://en.wikipedia.org/wiki/Top_post
>> Q: Were do I find info about this thing called top-posting?
>> A: Because it messes up the order in which people normally read text.
>> Q: Why is top-posting such a bad thing?
>> A: Top-posting.
>> Q: What is the most annoying thing in e-mail?
>>
>> A: No.
>> Q: Should I include quotations after my reply?
>>
>> http://daringfireball.net/2007/07/on_top
>>
Sorry for that,and thank you for the comment!I've learned it.
>> On Mon, Apr 28, 2025 at 05:51:08PM +0800, Zongmin Zhou wrote:
>>> Dear Greg and Shuah,
>>>
>>> I found out that the vhci-hcd driver added this virtual device
>>> as a platform device from the very beginning since 2014.
>>
>> Ah, I should have caught it back then, but at the time there really
>> wasn't another option.
>>
>
>>> I'm just getting in touch with this module and
>>> don't have a deep understanding of it，shuah should be clearer.
>
> faux_device should work fine for this. We do have to test of course.
>
> There are several examples of converting  platform device to faux device.
>
> 72239a78f9f5b9f05ea4bb7a15b92807906dab71
> dcd2a9a5550ef556c8fc11601a0f729fb71ead5d
>
Ok,I will learn to do it.
Thank you for your guidance.
>>
>> See the recent patches I did converting drivers to use the faux bus
>> code, it should be pretty simple to do.
>>
>>> I don't know if using the faux bus to replace the platform bus can 
>>> solve the
>>> problem that the error limitation on max_hw_sectors for usbip device
>>> since commit d74ffae8b8dd applied.
>>
>> That is for the storage driver, not usbip.  As the faux bus does not
>> have any real dma operations, this should cause it to work properly
>> given the default values involed, but that's up to you to test to verify
>> it does just that.  Try it and see!
>>
>>> But this change will request user to update kernel version to 
>>> support faux
>>> bus.
>>
>> That's just a normal kernel update to a newer version, what is wrong
>> with that?
>
> With one difference that the fix depends on faux_device feature - hence
> we can't apply it to stables. I do think it is the right direction to
> go to faux_device.
>
I just encountered similar users who were using a lower version of the 
kernel and were unwilling to upgrade.
But if reach a consensus to  go to faux_device,
I will try to make the change(converting platform device to faux device 
for vhci-hcd).
>>
>>> This will also be an expensive change to fix the problem?
>>
>> Fixing things properly is the correct thing to do in all cases.
>>
>
> Zongmin, do let me know if you are unable to make the change.
>
> thanks,
> -- Shuah