linux-kernel - RE: [PATCH v2] usb: chipidea: Hook into mux framework to toggle usb switch

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Date:   Fri, 20 Apr 2018 09:22:13 +0000
From:   Peter Chen <peter.chen@....com>
To:     Peter Rosin <peda@...ntia.se>,
        Yossi Mansharoff <yossim@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:CHIPIDEA USB HIGH SPEED DUAL ROLE CONTROLLER" 
        <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
CC:     "robh@...nel.org" <robh@...nel.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH v2] usb: chipidea: Hook into mux framework to toggle usb
 switch

 
> >> @@ -3,6 +3,8 @@ config USB_CHIPIDEA
> >>  	depends on ((USB_EHCI_HCD && USB_GADGET) || (USB_EHCI_HCD &&
> >> !USB_GADGET) || (!USB_EHCI_HCD && USB_GADGET)) && HAS_DMA
> >>  	select EXTCON
> >>  	select RESET_CONTROLLER
> >> +	select MULTIPLEXER
> >> +	select MUX_GPIO
> >
> > The above two configurations are only used at your specific platforms,
> > please add them at either your platform defconfig or the related hardware driver's
> Kconfig.
> 
> "select MUX_GPIO" is indeed questionable and should be somewhere else because
> this driver will work with any other mux as well. It's simply something else that
> requires it. If it was the case that MUX_GPIO is indeed required then the whole use
> of the mux subsystem is questionable and the thing controlled might as well be
> controlled directly with the GPIO line. The mux subsystem is good when a single mux
> "controller" is shared between several unrelated drivers utilizing different muxes
> controlled by that same mux "controller" (think several muxes controlled by the same
> GPIO line/lines). The mux subsystem is also useful when the driver does not want to
> handle/know how the specific mux is controlled. That said, it's of course not wrong to
> use the mux subsystem in cases like this either, but I think it might be much easier
> and direct to just twiddle the single GPIO line directly here?
> 
> Or do you expect some future HW variant that will use some other means to control
> this mux?
> 

No, this mux is only used at Yossi's boards, I expect these two configurations is under
MUX's hardware driver Kconfig if it is existed, or under its platform defconfig. Someone
has already complained too many selects increase the code size:

https://patchwork.kernel.org/patch/10349293/

> >>  	help
> >>  	  Say Y here if your system has a dual role high speed USB
> >>  	  controller based on ChipIdea silicon IP. It supports:
> >> diff --git a/drivers/usb/chipidea/core.c
> >> b/drivers/usb/chipidea/core.c index
> >> 33ae87f..8fa0991 100644
> >> --- a/drivers/usb/chipidea/core.c
> >> +++ b/drivers/usb/chipidea/core.c
> >> @@ -61,6 +61,7 @@
> >>  #include <linux/of.h>
> >>  #include <linux/regulator/consumer.h>  #include
> >> <linux/usb/ehci_def.h>
> >> +#include <linux/mux/consumer.h>
> >>
> >>  #include "ci.h"
> >>  #include "udc.h"
> >> @@ -687,6 +688,10 @@ static int ci_get_platdata(struct device *dev,
> >>  	if (of_find_property(dev->of_node, "non-zero-ttctrl-ttha", NULL))
> >>  		platdata->flags |= CI_HDRC_SET_NON_ZERO_TTHA;
> >>
> >> +	platdata->usb_switch = devm_mux_control_get_optional(dev, "usb_switch");
> >> +	if (IS_ERR(platdata->usb_switch))
> >> +		return PTR_ERR(platdata->usb_switch);
> >> +
> >>  	ext_id = ERR_PTR(-ENODEV);
> >>  	ext_vbus = ERR_PTR(-ENODEV);
> >>  	if (of_property_read_bool(dev->of_node, "extcon")) { diff --git
> >> a/drivers/usb/chipidea/host.c b/drivers/usb/chipidea/host.c index
> >> af45aa32..d9d2d00
> >> 100644
> >> --- a/drivers/usb/chipidea/host.c
> >> +++ b/drivers/usb/chipidea/host.c
> >> @@ -13,6 +13,7 @@
> >>  #include <linux/usb/hcd.h>
> >>  #include <linux/usb/chipidea.h>
> >>  #include <linux/regulator/consumer.h>
> >> +#include <linux/mux/consumer.h>
> >>
> >>  #include "../host/ehci.h"
> >>
> >> @@ -161,6 +162,10 @@ static int host_start(struct ci_hdrc *ci)
> >>  		if (ci_otg_is_fsm_mode(ci)) {
> >>  			otg->host = &hcd->self;
> >>  			hcd->self.otg_port = 1;
> >> +		} else {
> >> +			ret = mux_control_select(ci->platdata->usb_switch, 1);
> >> +			if (ret)
> >> +				goto disable_reg;
> >
> > What will happen if ci->platdata->usb_switch  is NULL?
> 
> What has not been mentioned in this patch is that it depends on another patch which
> is not yet upstream. You can google for
> 
> mux: add mux_control_get_optional() API
> 
> to get an idea (it's also in linux-next). Anyway, with that patch this is not a problem.
> 

Thanks, I see it judges NULL pointer, then it is OK.

 
> >>  /**
> >>   * struct ci_hdrc_cable - structure for external connector cable
> >> state tracking @@ -
> >> 76,6 +77,7 @@ struct ci_hdrc_platform_data {
> >>  	/* VBUS and ID signal state tracking, using extcon framework */
> >>  	struct ci_hdrc_cable		vbus_extcon;
> >>  	struct ci_hdrc_cable		id_extcon;
> >> +	struct mux_control		*usb_switch;
> >>  	u32			phy_clkgate_delay_us;
> >
> > If CONFIG_USB_CHIPIDEA_HOST is not defined, it may cause build error
> 
> How is that related? There is a forward declaration above?
> 

Sorry, I did not notice drivers/usb/chipidea/core.c also includes <linux/mux/consumer.h>.

Peter