linux-kernel - USB: DMA: mapping existing buffer is not supported?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 14 Sep 2023 03:06:58 +0800
From:   Randy Li <ayaka@...lik.info>
To:     gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-kernel@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org
Subject: USB: DMA: mapping existing buffer is not supported?

Hello

I was trying to understand why USB webcams (UVC) have to copy video data 
through the CPU (uvc_video_complete() schedules 
uvc_video_copy_data_work() for this purpose). During my investigation, I 
noticed that functions like|usb_sg_*() and |usb_buffer_*() are not 
available since kernel version 2.6.12.

I can comprehend that USB host controllers such as xHCI, commonly found 
in embedded implementations like dwc3, do not support IOMMU. However, 
this should not prevent them from operating on a contiguous buffer.

If the USB subsystem can no longer work with existing buffers, I propose 
that we consider removing the remaining documentation in the "Working 
with existing buffers" section of Documentation/driver-api/usb/dma.rst.

Sincerely

Randy