[PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Prashanth K]

Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
drawn from Vbus to be up to 500mA. However USB gadget operating
in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
ConfigFS takes its default value from this config. Hence increase
the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.

Signed-off-by: Prashanth K <prashanth.k@oss.qualcomm.com>
---
 drivers/usb/gadget/Kconfig | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index 76521555e3c1..904652c37385 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -97,8 +97,8 @@ config USB_GADGET_DEBUG_FS
 	   to conserve kernel memory, say "N".
 
 config USB_GADGET_VBUS_DRAW
-	int "Maximum VBUS Power usage (2-500 mA)"
-	range 2 500
+	int "Maximum VBUS Power usage (2-900 mA)"
+	range 2 900
 	default 2
 	help
 	   Some devices need to draw power from USB when they are
@@ -107,8 +107,11 @@ config USB_GADGET_VBUS_DRAW
 	   such as an AC adapter or batteries.
 
 	   Enter the maximum power your device draws through USB, in
-	   milliAmperes.  The permitted range of values is 2 - 500 mA;
-	   0 mA would be legal, but can make some hosts misbehave.
+	   milliAmperes. The permitted range of values depends on the
+	   connection speed, for SuperSpeed and higher it's 2 - 900 mA,
+	   but connections with High-Speed or slower can draw power
+	   ranging from 2 - 500 mA; 0 mA would be legal, but can make
+	   some hosts misbehave.
 
 	   This value will be used except for system-specific gadget
 	   drivers that have more specific information.
-- 
2.25.1

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Alan Stern]

On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
> drawn from Vbus to be up to 500mA. However USB gadget operating
> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
> ConfigFS takes its default value from this config. Hence increase
> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.

Is this the sort of thing that really needs to be a Kconfig option?  Why 
not make the decision at runtime, based on the needs of the gadget or 
function drivers and the connection speed?

Alan Stern

> Signed-off-by: Prashanth K <prashanth.k@oss.qualcomm.com>
> ---
>  drivers/usb/gadget/Kconfig | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
> index 76521555e3c1..904652c37385 100644
> --- a/drivers/usb/gadget/Kconfig
> +++ b/drivers/usb/gadget/Kconfig
> @@ -97,8 +97,8 @@ config USB_GADGET_DEBUG_FS
>  	   to conserve kernel memory, say "N".
>  
>  config USB_GADGET_VBUS_DRAW
> -	int "Maximum VBUS Power usage (2-500 mA)"
> -	range 2 500
> +	int "Maximum VBUS Power usage (2-900 mA)"
> +	range 2 900
>  	default 2
>  	help
>  	   Some devices need to draw power from USB when they are
> @@ -107,8 +107,11 @@ config USB_GADGET_VBUS_DRAW
>  	   such as an AC adapter or batteries.
>  
>  	   Enter the maximum power your device draws through USB, in
> -	   milliAmperes.  The permitted range of values is 2 - 500 mA;
> -	   0 mA would be legal, but can make some hosts misbehave.
> +	   milliAmperes. The permitted range of values depends on the
> +	   connection speed, for SuperSpeed and higher it's 2 - 900 mA,
> +	   but connections with High-Speed or slower can draw power
> +	   ranging from 2 - 500 mA; 0 mA would be legal, but can make
> +	   some hosts misbehave.
>  
>  	   This value will be used except for system-specific gadget
>  	   drivers that have more specific information.
> -- 
> 2.25.1
> 
> 

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Prashanth K]

On 20-01-25 08:17 pm, Alan Stern wrote:
> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
>> drawn from Vbus to be up to 500mA. However USB gadget operating
>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
>> ConfigFS takes its default value from this config. Hence increase
>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
> 
> Is this the sort of thing that really needs to be a Kconfig option?  Why 
> not make the decision at runtime, based on the needs of the gadget or 
> function drivers and the connection speed?
> 
> Alan Stern
> 

Right, set_config() in composite.c does this in runtime based on the
values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
If we don't set MaxPower from configFS, this config helps to set it
during compile time. In fact MaxPower in configFS takes its default
value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
has this limitation where it's only allowing values upto 500mA.

Regards,
Prashanth K

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Alan Stern]

On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
> 
> 
> On 20-01-25 08:17 pm, Alan Stern wrote:
> > On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
> >> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
> >> drawn from Vbus to be up to 500mA. However USB gadget operating
> >> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
> >> ConfigFS takes its default value from this config. Hence increase
> >> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
> > 
> > Is this the sort of thing that really needs to be a Kconfig option?  Why 
> > not make the decision at runtime, based on the needs of the gadget or 
> > function drivers and the connection speed?
> > 
> > Alan Stern
> > 
> 
> Right, set_config() in composite.c does this in runtime based on the
> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
> If we don't set MaxPower from configFS, this config helps to set it
> during compile time. In fact MaxPower in configFS takes its default
> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
> has this limitation where it's only allowing values upto 500mA.

Why does MaxPower need to be set at compile time?  Why not set it at 
runtime instead?

If MaxPower gets set at runtime then it can take its default value to be 
500 mA or 900 mA depending on the connection speed.  There will be no 
need for CONFIG_USB_GAGDGET_VBUS_DRAW.

You are trying to improve a compile-time limitation on a quantity which 
isn't known until runtime.  The whole idea of doing it that way is 
fundamentally wrong.  You shouldn't try to improve it a little, you 
should fix the basic mistake by doing everything at runtime.

Alan Stern

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Prashanth K]

On 21-01-25 08:36 pm, Alan Stern wrote:
> On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
>>
>>
>> On 20-01-25 08:17 pm, Alan Stern wrote:
>>> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
>>>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
>>>> drawn from Vbus to be up to 500mA. However USB gadget operating
>>>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
>>>> ConfigFS takes its default value from this config. Hence increase
>>>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
>>>
>>> Is this the sort of thing that really needs to be a Kconfig option?  Why 
>>> not make the decision at runtime, based on the needs of the gadget or 
>>> function drivers and the connection speed?
>>>
>>> Alan Stern
>>>
>>
>> Right, set_config() in composite.c does this in runtime based on the
>> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
>> If we don't set MaxPower from configFS, this config helps to set it
>> during compile time. In fact MaxPower in configFS takes its default
>> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
>> has this limitation where it's only allowing values upto 500mA.
> 
> Why does MaxPower need to be set at compile time?  Why not set it at 
> runtime instead?
> 
> If MaxPower gets set at runtime then it can take its default value to be 
> 500 mA or 900 mA depending on the connection speed.  There will be no 
> need for CONFIG_USB_GAGDGET_VBUS_DRAW.
> 

Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and
maybe also avoid configfs/composite from using it?

> You are trying to improve a compile-time limitation on a quantity which 
> isn't known until runtime.  The whole idea of doing it that way is 
> fundamentally wrong.  You shouldn't try to improve it a little, you 
> should fix the basic mistake by doing everything at runtime.
> 
> Alan Stern
> 
Regards,
Prashanth K

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Alan Stern]

On Tue, Jan 21, 2025 at 10:19:08PM +0530, Prashanth K wrote:
> 
> 
> On 21-01-25 08:36 pm, Alan Stern wrote:
> > On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
> >>
> >>
> >> On 20-01-25 08:17 pm, Alan Stern wrote:
> >>> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
> >>>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
> >>>> drawn from Vbus to be up to 500mA. However USB gadget operating
> >>>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
> >>>> ConfigFS takes its default value from this config. Hence increase
> >>>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
> >>>
> >>> Is this the sort of thing that really needs to be a Kconfig option?  Why 
> >>> not make the decision at runtime, based on the needs of the gadget or 
> >>> function drivers and the connection speed?
> >>>
> >>> Alan Stern
> >>>
> >>
> >> Right, set_config() in composite.c does this in runtime based on the
> >> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
> >> If we don't set MaxPower from configFS, this config helps to set it
> >> during compile time. In fact MaxPower in configFS takes its default
> >> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
> >> has this limitation where it's only allowing values upto 500mA.
> > 
> > Why does MaxPower need to be set at compile time?  Why not set it at 
> > runtime instead?
> > 
> > If MaxPower gets set at runtime then it can take its default value to be 
> > 500 mA or 900 mA depending on the connection speed.  There will be no 
> > need for CONFIG_USB_GAGDGET_VBUS_DRAW.
> > 
> 
> Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and
> maybe also avoid configfs/composite from using it?

Indeed, the whole idea is to avoid using CONFIG_USB_GADGET_VBUS_DRAW in 
configfs and composite.

If nothing will still be using it, just remove it entirely.  No need to 
mark it as legacy.

Alan Stern

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Prashanth K]

On 22-01-25 12:56 am, Alan Stern wrote:
> On Tue, Jan 21, 2025 at 10:19:08PM +0530, Prashanth K wrote:
>>
>>
>> On 21-01-25 08:36 pm, Alan Stern wrote:
>>> On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
>>>>
>>>>
>>>> On 20-01-25 08:17 pm, Alan Stern wrote:
>>>>> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
>>>>>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
>>>>>> drawn from Vbus to be up to 500mA. However USB gadget operating
>>>>>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
>>>>>> ConfigFS takes its default value from this config. Hence increase
>>>>>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
>>>>>
>>>>> Is this the sort of thing that really needs to be a Kconfig option?  Why 
>>>>> not make the decision at runtime, based on the needs of the gadget or 
>>>>> function drivers and the connection speed?
>>>>>
>>>>> Alan Stern
>>>>>
>>>>
>>>> Right, set_config() in composite.c does this in runtime based on the
>>>> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
>>>> If we don't set MaxPower from configFS, this config helps to set it
>>>> during compile time. In fact MaxPower in configFS takes its default
>>>> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
>>>> has this limitation where it's only allowing values upto 500mA.
>>>
>>> Why does MaxPower need to be set at compile time?  Why not set it at 
>>> runtime instead?
>>>
>>> If MaxPower gets set at runtime then it can take its default value to be 
>>> 500 mA or 900 mA depending on the connection speed.  There will be no 
>>> need for CONFIG_USB_GAGDGET_VBUS_DRAW.
>>>
>>
>> Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and
>> maybe also avoid configfs/composite from using it?
> 
> Indeed, the whole idea is to avoid using CONFIG_USB_GADGET_VBUS_DRAW in 
> configfs and composite.
> 
> If nothing will still be using it, just remove it entirely.  No need to 
> mark it as legacy.
> 
> Alan Stern

Sure, let me work on that and send a v2 (or another patch). Thanks for
the feedback.

Regards,
Prashanth K

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Prashanth K]

On 22-01-25 12:56 am, Alan Stern wrote:
> On Tue, Jan 21, 2025 at 10:19:08PM +0530, Prashanth K wrote:
>>
>>
>> On 21-01-25 08:36 pm, Alan Stern wrote:
>>> On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
>>>>
>>>>
>>>> On 20-01-25 08:17 pm, Alan Stern wrote:
>>>>> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
>>>>>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
>>>>>> drawn from Vbus to be up to 500mA. However USB gadget operating
>>>>>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
>>>>>> ConfigFS takes its default value from this config. Hence increase
>>>>>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
>>>>>
>>>>> Is this the sort of thing that really needs to be a Kconfig option?  Why 
>>>>> not make the decision at runtime, based on the needs of the gadget or 
>>>>> function drivers and the connection speed?
>>>>>
>>>>> Alan Stern
>>>>>
>>>>
>>>> Right, set_config() in composite.c does this in runtime based on the
>>>> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
>>>> If we don't set MaxPower from configFS, this config helps to set it
>>>> during compile time. In fact MaxPower in configFS takes its default
>>>> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
>>>> has this limitation where it's only allowing values upto 500mA.
>>>
>>> Why does MaxPower need to be set at compile time?  Why not set it at 
>>> runtime instead?
>>>
>>> If MaxPower gets set at runtime then it can take its default value to be 
>>> 500 mA or 900 mA depending on the connection speed.  There will be no 
>>> need for CONFIG_USB_GAGDGET_VBUS_DRAW.
>>>
>>
>> Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and
>> maybe also avoid configfs/composite from using it?
> 
> Indeed, the whole idea is to avoid using CONFIG_USB_GADGET_VBUS_DRAW in 
> configfs and composite.
> 
> If nothing will still be using it, just remove it entirely.  No need to 
> mark it as legacy.
> 
> Alan Stern

Hi Alan, small doubt, I see that gadget/legacy/webcam.c is a super-speed
gadget which uses CONFIG_USB_GADGET_VBUS_DRAW. I'm quite not really sure
if anyone uses it now, but if someone uses it, then wouldn't my patch be
applicable there?

Noticed this while preparing a patch to remove dependency of VBUS_DRAW
config from configfs/composite layer. Its ready, will send that after
some testing.

Regards,
Prashanth K

Re: [PATCH] usb: gadget: Increase the limit of USB_GADGET_VBUS_DRAW to 900mA

[Alan Stern]

On Thu, Feb 20, 2025 at 09:47:58AM +0530, Prashanth K wrote:
> 
> 
> On 22-01-25 12:56 am, Alan Stern wrote:
> > On Tue, Jan 21, 2025 at 10:19:08PM +0530, Prashanth K wrote:
> >>
> >>
> >> On 21-01-25 08:36 pm, Alan Stern wrote:
> >>> On Tue, Jan 21, 2025 at 09:50:08AM +0530, Prashanth K wrote:
> >>>>
> >>>>
> >>>> On 20-01-25 08:17 pm, Alan Stern wrote:
> >>>>> On Mon, Jan 20, 2025 at 04:47:02PM +0530, Prashanth K wrote:
> >>>>>> Currently CONFIG_USB_GADGET_VBUS_DRAW limits the maximum current
> >>>>>> drawn from Vbus to be up to 500mA. However USB gadget operating
> >>>>>> in SuperSpeed or higher can draw up to 900mA. Also, MaxPower in
> >>>>>> ConfigFS takes its default value from this config. Hence increase
> >>>>>> the allowed range of CONFIG_USB_GADGET_VBUS_DRAW to 900mA.
> >>>>>
> >>>>> Is this the sort of thing that really needs to be a Kconfig option?  Why 
> >>>>> not make the decision at runtime, based on the needs of the gadget or 
> >>>>> function drivers and the connection speed?
> >>>>>
> >>>>> Alan Stern
> >>>>>
> >>>>
> >>>> Right, set_config() in composite.c does this in runtime based on the
> >>>> values of MaxPower (from configFS), VBUS_DRAW defconfig and speed.
> >>>> If we don't set MaxPower from configFS, this config helps to set it
> >>>> during compile time. In fact MaxPower in configFS takes its default
> >>>> value from CONFIG_USB_GADGET_VBUS_DRAW . Sent this patch because Kconfig
> >>>> has this limitation where it's only allowing values upto 500mA.
> >>>
> >>> Why does MaxPower need to be set at compile time?  Why not set it at 
> >>> runtime instead?
> >>>
> >>> If MaxPower gets set at runtime then it can take its default value to be 
> >>> 500 mA or 900 mA depending on the connection speed.  There will be no 
> >>> need for CONFIG_USB_GAGDGET_VBUS_DRAW.
> >>>
> >>
> >> Yes, agreed. Can we mark CONFIG_USB_GAGDGET_VBUS_DRAW as legacy and
> >> maybe also avoid configfs/composite from using it?
> > 
> > Indeed, the whole idea is to avoid using CONFIG_USB_GADGET_VBUS_DRAW in 
> > configfs and composite.
> > 
> > If nothing will still be using it, just remove it entirely.  No need to 
> > mark it as legacy.
> > 
> > Alan Stern
> 
> Hi Alan, small doubt, I see that gadget/legacy/webcam.c is a super-speed
> gadget which uses CONFIG_USB_GADGET_VBUS_DRAW. I'm quite not really sure
> if anyone uses it now, but if someone uses it, then wouldn't my patch be
> applicable there?

A quick search shows that the legacy/gmidi.c driver also uses it.

Still, if these are the only drivers that uses 
CONFIG_USB_GADGET_VBUS_DRAW, it means that parameter isn't really very 
useful.

The best solution I can think of is to make vbus_draw a module parameter 
in for the two drivers, with the default set to 500.  That's more 
flexible than relying on a Kconfig parameter anyway.  Of course, this 
means the .MaxPower field in the webcam_config_driver and midi_config 
structures will have to be set dynamically at runtime.

Alan Stern

> Noticed this while preparing a patch to remove dependency of VBUS_DRAW
> config from configfs/composite layer. Its ready, will send that after
> some testing.
> 
> Regards,
> Prashanth K