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

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Message-ID: <4c6660a6-29ce-4b97-b092-8fc15585e52a@163.com>
Date: Fri, 25 Apr 2025 16:08:47 +0800
From: Zongmin Zhou <min_halo@....com>
To: Christoph Hellwig <hch@...radead.org>, gregkh@...uxfoundation.org,
 Shuah Khan <skhan@...uxfoundation.org>
Cc: 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

Dear Greg and Christoph:

This patch is the simple solution for the issue described in below link:
https://lore.kernel.org/all/20250219092555.112631-1-min_halo@163.com/

This issue has been discussed at length with Shuah.

As Christoph said,vhci-hcd is a virtual hci,
but it serves as a bridge to connect virtual USB devices to the real USB 
controller.
Since the commit d74ffae8b8dd is applied on kernel v5.3,
the virtual USB devices's max_sectors size is limited since v5.3.

Just because on vhci-hcd, the dma mask setting follows the platform 
device default setting(32-bit).

So I want to get the real USB controller dma mask to set on vhci-hcd 
driver，
or set to 64 by default,to fix the max_sectors limited issue
on virtual USB device since the commit d74ffae8b8dd applied.

Thanks.

On 2025/4/22 15:24, Christoph Hellwig wrote:
> On Tue, Apr 22, 2025 at 02:34:09PM +0800, Zongmin Zhou wrote:
>> From: Zongmin Zhou <zhouzongmin@...inos.cn>
>>
>> fix usb device limited  max_sectors when use usbip protocol
> As far as I can tell this is a virtual HCI and can't perform DMA.
> Thus nothing should use DMA API calls on it and the mask is irrelevant.