On Tue, 10 Aug, 2021, 7:50 pm Oliver Neukum, <oneu...@suse.com> wrote:
> > On 10.08.21 16:13, Muni Sekhar wrote: > > On Mon, Aug 9, 2021 at 1:45 PM Oliver Neukum <oneu...@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-pher...@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. Any other examples of devices associated with the USB bus? Do we have any reference driver in the mainline kernel tree? Does lsusb reports these devices? > > 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 > > >
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