From: Alan Stern <stern@rowland.harvard.edu>
To: Alexander Dahl <ada@thorsis.com>
Cc: linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, rca@thorsis.com
Subject: Re: Enable HSIC Host Port on Atmel/Microchip SAMA5D2
Date: Mon, 23 Aug 2021 10:00:52 -0400 [thread overview]
Message-ID: <20210823140052.GA120849@rowland.harvard.edu> (raw)
In-Reply-To: <2869763.XZdSvA6Ref@ada>
On Mon, Aug 23, 2021 at 11:24:35AM +0200, Alexander Dahl wrote:
> Hello,
>
> for a new embedded board featuring a Microchip SAMA5D2 SoC (64 MiB SiP variant
> SAMA5D27C-D5M) we connected the third USB host port (HSIC only) with an
> USB3503 hub chip. This doesn't work out of the box with the Linux kernel
> currently, because neither the SoC nor the kernel does enable the HSIC
> interface by default.
>
> That SoC has three USB host ports, from the SAMA5D2 Series Datasheet [1] I
> learned there's a flag in an EHCI register, which has to be set to enable the
> HSIC interface on port C, the third port. (Section "41.7.14 EHCI: REG08 - HSIC
> Enable/Disable" of the datasheet.) I suppose that register is vendor specific.
> The register definitions in '/include/linux/usb/ehci_def.h' do not contain
> that register.
>
> Where would I add that register definition and set that flag in the kernel
> then? I suppose in the vendor specific ehci driver?
> That would be 'drivers/usb/host/ehci-atmel.c' right?
That is where you would set the flag. You might want to put the
register definition in ehci_def.h, with the other definitions.
> Since that feature is optional (other boards don't need to turn on hsic on
> that port), some driver specific new device tree binding would be necessary,
> right? I suppose that would have to be documented in 'Documentation/
> devicetree/bindings/usb/atmel-usb.txt' right? (Or that would have to be
> converted to yaml first?)
Yes, it would have to go into the device tree data somehow. I don't
know the best way to do this; people who know more about DT may be able
to tell you.
> Is this the right track? If yes, I'm going to develop patches for this.
> Otherwise any hint into the right direction are highly appreciated.
Yes, this is the right approach.
Alan Stern
> FWIW, I'm not the first one struggling [2] with this problem. ;-)
>
> Greets
> Alex
>
> [1] https://www.microchip.com/en-us/product/ATSAMA5D27C-D5M#document-table
> [2] https://community.atmel.com/forum/sama5d2-using-hsic-under-linux
next prev parent reply other threads:[~2021-08-23 14:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-23 9:24 Enable HSIC Host Port on Atmel/Microchip SAMA5D2 Alexander Dahl
2021-08-23 14:00 ` Alan Stern [this message]
2021-08-24 6:37 ` [RFC PATCH] USB: host: ehci-atmel: Allow enabling HSIC on SAMA5D2 Alexander Dahl
2021-08-24 6:45 ` Greg Kroah-Hartman
2021-09-02 15:33 ` Nicolas Ferre
2021-09-06 7:20 ` Alexander Dahl
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