Re: [PATCH v3 6/6] phy: exynos5-usbdrd: support Exynos USBDRD 3.1 combo phy (HS & SS)

[William McVicker <willmcvicker@google.com>]

On 06/17/2024, André Draszik wrote:
> Add support for the Exynos USB 3.1 DRD combo phy, as found in Exynos 9
> SoCs like Google GS101. It supports USB SS, HS and DisplayPort.
> 
> In terms of UTMI+, this is very similar to the existing Exynos850
> support in this driver. The difference is that this combo phy supports
> both UTMI+ (HS) and PIPE3 (SS). It also supports DP alt mode.
> 
> The number of ports for UTMI+ and PIPE3 can be determined using the
> LINKPORT register (which also exists on Exynos E850).
> 
> For SuperSpeed (SS) a new SS phy is in use and its PIPE3 interface is
> new compared to Exynos E850, and also very different from the existing
> support for older Exynos SoCs in this driver.
> 
> The SS phy needs a bit more configuration work and register tuning for
> signal quality to work reliably, presumably due to the higher
> frequency, e.g. to account for different board layouts. Additionally,
> power needs to be enabled before writing to the SS phy registers.
> 
> This commit adds the necessary changes for USB HS and SS to work.
> DisplayPort is out of scope in this commit.
> 
> Notes:
> * For the register tuning, exynos5_usbdrd_apply_phy_tunes() has been
>   added with the appropriate data structures to support tuning at
>   various stages during initialisation. Since these are hardware
>   specific, the platform data is supposed to be populated accordingly.
>   The implementation is loosely modelled after the Samsung UFS PHY
>   driver.
> 
>   There is one tuning state for UTMI+, PTS_UTMI_POSTINIT, to execute
>   after init and generally intended for HS signal tuning, as done in
>   this commit.
> 
>   PTS_PIPE3_PREINIT PTS_PIPE3_INIT PTS_PIPE3_POSTINIT
>   PTS_PIPE3_POSTLOCK are tuning states for PIPE3. In the downstream
>   driver, preinit differs by Exynos SoC, and postinit and postlock
>   are different per board. The latter haven't been implemented for
>   gs101 here, because downstream doesn't use them on gs101 either.
> 
> * Signal lock acquisition for SS depends on the orientation of the
>   USB-C plug. Since there currently is no infrastructure to chain
>   connector events to both the USB DWC3 driver and this phy driver, a
>   work-around has been added in
>   exynos5_usbdrd_usbdp_g2_v4_pma_check_cdr_lock() to check both
>   registers if it failed in one of the orientations.
> 
> * Equally, we can only establish SS speed in one of the connector
>   orientations due to programming differences when selecting the lane
>   mux in exynos5_usbdrd_usbdp_g2_v4_pma_lane_mux_sel(), which really
>   needs to be dynamic, based on the orientation of the connector.
> 
> * As is, we can establish a HS link using any cable, and an SS link in
>   one orientation of the plug, falling back to HS if the orientation is
>   reversed to the expectation.
> 
> Signed-off-by: André Draszik <andre.draszik@linaro.org>

Tested-by: Will McVicker <willmcvicker@google.com>

[...]

Thanks,
Will