On Tue, Nov 16, 2021 at 09:21:44PM -0500, Alan Stern wrote:

On Tue, Nov 16, 2021 at 12:07:39PM -0800, Matthias Kaehlcke wrote:

quoted

Some USB controller drivers that depend on the xhci-plat driver
specify this dependency using 'select' in Kconfig. This is not
recommended for symbols that have other dependencies as it may
lead to invalid configurations. Use 'depends on' to specify the
dependency instead of 'select'.

For dwc3 specify the dependency on USB_XHCI_PLATFORM in
USB_DWC3_HOST and USB_DWC3_DUAL_ROLE. Also adjust the
dependencies of USB_DWC3_CORE to make sure that at least one
of USB_DWC3_HOST, USB_DWC3_GADGET or USB_DWC3_DUAL_ROLE can be
selected.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---

Changes in v17:
- removed explicit dependency on USB from USB_DWC3
- added 'Reviewed-by' tags from Roger and Doug

Changes in v16:
- none

Changes in v15:
- adjusted dependencies of USB_DWC3_CORE to make sure it can only
  be enabled when at least one of USB_DWC3_HOST, USB_DWC3_GADGET
  or USB_DWC3_DUAL_ROLE is selectable
- updated commit message

Changes in v14:
- none

Changes in v13:
- patch added to the series

quoted

diff --git a/drivers/usb/host/Kconfig b/drivers/usb/host/Kconfig
index d1d926f8f9c2..e5e612f143a1 100644
--- a/drivers/usb/host/Kconfig
+++ b/drivers/usb/host/Kconfig

@@ -80,7 +80,7 @@ config USB_XHCI_MTK
 
 config USB_XHCI_MVEBU
 	tristate "xHCI support for Marvell Armada 375/38x/37xx"
-	select USB_XHCI_PLATFORM
+	depends on USB_XHCI_PLATFORM
 	depends on HAS_IOMEM
 	depends on ARCH_MVEBU || COMPILE_TEST
 	help

@@ -112,9 +112,9 @@ config USB_EHCI_BRCMSTB
 config USB_BRCMSTB
 	tristate "Broadcom STB USB support"
 	depends on (ARCH_BRCMSTB && PHY_BRCM_USB) || COMPILE_TEST
+	depends on !USB_XHCI_HCD || USB_XHCI_PLATFORM
 	select USB_OHCI_HCD_PLATFORM if USB_OHCI_HCD
 	select USB_EHCI_BRCMSTB if USB_EHCI_HCD
-	select USB_XHCI_PLATFORM if USB_XHCI_HCD
 	help
 	  Enables support for XHCI, EHCI and OHCI host controllers
 	  found in Broadcom STB SoC's.

It should be pointed out that this now requires people with xHCI systems 
to actively turn on CONFIG_USB_XHCI_PLATFORM before they can enable 
CONFIG_USB_BRCMSTB.  Before, that was not necessary.  Some users might 
get confused and not realize what is needed.  Perhaps something should 
be added to the "help" text.

I agree that the change could cause confusion, I'm not sure though if
adding something to the "help" text is a good mitigation. Users won't see
the text unless they can select the option, which requires
CONFIG_USB_XHCI_PLATFORM to be enabled. Also the dependencies are specified
nearby (and displayed), so it seems similar to a code comment on something
that the code evidently does (e.g. "initialize foobar with 0").

On a different note: I'm considering to break the CONFIG_USB_XHCI_PLATFORM
related patches out of the onboard_usb_hub series, since the driver
doesn't any longer depend on xhci_plat. In that sense I'm also open
to abandon those patches, if they aren't considered an improvement on
their own.

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