linux-kernel - Re: [PATCH 8/8] arm64: dts: exynos: Enable USB support on E850-96 board

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Date:   Sat, 19 Aug 2023 10:36:10 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc:     JaeHun Jung <jh0801.jung@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 8/8] arm64: dts: exynos: Enable USB support on E850-96
 board

On 19/08/2023 05:17, Sam Protsenko wrote:
> The E850-96 board has a micro-USB socket and two USB 2.0 host sockets.
> The USB role (host or peripheral) is selected automatically depending on
> micro-USB cable attachment state:
>   - micro-USB cable is attached: USB device role
>   - micro-USB cable is detached: USB host role
> 
> USB can't act simultaneously as a device and a host, because Exynos850
> SoC has only one USB controller and there are no external USB
> controllers on the E850-96 board. So the USB switch chip (specifically
> TS3USB221A) connects SoC USB lines either to micro-USB connector or to
> USB hub chip (LAN9514), w.r.t. micro-USB cable attachment state.
> 
> When USB works in the host role, Ethernet capability becomes available
> too, as LAN9514 chip (providing USB hub) also enables Ethernet PHY and
> Ethernet MAC.
> 
> Dynamic role switching is done in gpio-usb-b-connector, using current
> micro-USB VBUS line level as a trigger:
>   - VBUS=high: SoC USB lines are wired to micro-USB socket
>   - VBUS=low: SoC USB lines are wired to USB hub chip
> 
> In order to make USB host functional when the board is booted with
> micro-USB cable disconnected, role-switch-default-mode = "host" is used.
> 
> One can look at E850-96 board schematics [1] to figure out how exactly
> all related USB hardware connections and lines reflect into
> corresponding device tree definitions.
> 
> As PMIC regulators are not implemented yet, we rely on USB LDOs being
> already enabled in the bootloader, and a dummy regulator is provided to
> "usbdrd" vdd nodes for now.
> 
> [1] https://www.96boards.org/documentation/consumer/e850-96b/hardware-docs/
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> ---
>  .../boot/dts/exynos/exynos850-e850-96.dts     | 58 +++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 

This looks good. Please split the DTS patches from the patchset, so they
won't be applied by Greg. Anyway, I finished pulling for this cycle, so
this will have to wait till v6.6-rc1.

Best regards,
Krzysztof