On 04/05/16 21:45, Marek Vasut wrote:
On 04/05/2016 07:35 PM, Stephen Warren wrote:
On 04/05/2016 10:36 AM, Semen Protsenko wrote:
From: Sam Protsenko <semen.protse...@linaro.org>
The description was borrowed from kernel, but allowed range was changed
from 2..500 to 0..500, because some boards require this option to be 0.
Do they /require/ the value to be 0, or simply currently have it set to
0 because whoever set the value in U-Boot wasn't aware that a value of 0
could cause issues with some hosts?
For TBS2910 I set the value to 0 because the board does not need any power
from the host. It is always self-powered and cannot be driven from USB.
And yes, I was not aware that a value of 0 could cause problems.
I'd be tempted to keep the same range as the Linux kernel and bump all
boards up to a minimum value of 2.
Right. VBUS draw 0 might confuse some non-Linux systems.
Presumably there's some good reason
the kernel chose a minimum of 2, and in practice I expect increasing all
boards to 2 isn't going to make any negative difference.
diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
+config USB_GADGET_VBUS_DRAW
+ int "Maximum VBUS Power usage (2-500 mA)"
+ range 0 500
+ default 2
+ help
+ Some devices need to draw power from USB when they are
+ configured, perhaps to operate circuitry or to recharge
+ batteries. This is in addition to any local power supply,
+ 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.
In particular, I'm thinking of that last sentence.
Is the problematic value of zero forbidden in some spec, or is actually
a bug in the host driver (to be fixed there) causing confusion?
On the other hand, if no bus power is needed a maximum power value of 2mA
should not hurt.
Regards,
Soeren
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