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From: Oliver Neukum <oneukum@suse.com>
To: Muni Sekhar <munisekharrms@gmail.com>, Oliver Neukum <oneukum@suse.com>
Cc: kernelnewbies <kernelnewbies@kernelnewbies.org>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: read() via USB bus
Date: Tue, 10 Aug 2021 16:20:03 +0200	[thread overview]
Message-ID: <4e7c9279-805c-c236-c048-2b817b1a7c3c@suse.com> (raw)
In-Reply-To: <CAHhAz+i5YeQdJnBH6BvMJ-B0DtoBu9ER4Z79CPOfX5NuFvO=bA@mail.gmail.com>


On 10.08.21 16:13, Muni Sekhar wrote:
> On Mon, Aug 9, 2021 at 1:45 PM Oliver Neukum <oneukum@suse.com> wrote:
>>
>> 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.
> I am referring to the code mentioned in
> https://patchwork.kernel.org/project/linux-arm-msm/patch/1534464348-8227-3-git-send-email-pheragu@codeaurora.org/
>
> As per this driver gets access to the Qcomm’s USB h/w device registers
> via devm_extcon_dev_allocate(), devm_extcon_dev_register(),
> platform_get_resource() and devm_ioremap_resource API’s.
>
> What does the USB external connector EXTCON_USB \ EXTCON_USB_HOST
> devices means? Are these different from normal USB devices?
>
Hi,

those are not USB devices. Those are devices associated with a USB bus
and are to be
found on the host's CPU's bus. This is like a graphics card is from the
driver's view
not a DisplayPort device or a SCSI controller is not a SCSI device for
its driver.

A host controller and associated devices can be on any bus. Such
controllers follow
their separate specifications and how they are to be driven is strictly
speaking
not part of USB:

    Regards
        Oliver



  reply	other threads:[~2021-08-10 14:25 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09  7:58 Muni Sekhar
2021-08-09  8:15 ` Oliver Neukum
2021-08-09  8:44   ` Greg KH
2021-08-12  9:45     ` LDD 3rd ed. - It was: " Fabio M. De Francesco
2021-08-12 10:13       ` Valdis Klētnieks
2021-08-12 10:18       ` Greg KH
2021-08-12 10:26         ` Robert P. J. Day
2021-08-09 16:19   ` Muni Sekhar
2021-08-10 14:13   ` Muni Sekhar
2021-08-10 14:20     ` Oliver Neukum [this message]
     [not found]       ` <CAHhAz+ioThu3v4VW6LVqFn9MhgNaqv=qDoxh8Orkw2LOEC_JYA@mail.gmail.com>
2021-08-11 10:04         ` Oliver Neukum

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