linux-kernel - Re: read() via USB bus

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Message-ID: <8923f2b8-0be0-ffbf-70a4-c03c9a02d58a@suse.com>
Date:   Mon, 9 Aug 2021 10:15:29 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Muni Sekhar <munisekharrms@...il.com>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: read() via USB bus

On 09.08.21 09:58, Muni Sekhar wrote:
> Hi all,
>
> PCIe memory mapped registers can be read via readb(), readw(), readl()
> kernel API's. Similarly what are the kernel API to read the device
> registers via USB bus
>

Hi,

I am afraid this is based on a fundamental misunderstanding on how
USB works. It is based on passing messages, not reading and writing
registers.

USB devices are primarily based on endpoints, not registers. A literal
answer to your question would point you to the clear/set/get_feature
standard requests of chapter 9 of the specification, but that really
will not help you, as you are making assumption that fundamentally
do not apply.

I hope this list stays friendly to newcomers and we will answer
specific questions, but at this point I must advise you to first
read an introductory book.

    HTH
        Oliver