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From: Alan Stern <stern@rowland.harvard.edu>
To: Nicolas Boichat <drinkcat@chromium.org>
Cc: linux-usb@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Eugene Korenevsky <ekorenevsky@gmail.com>,
	Peter Chen <peter.chen@nxp.com>,
	Daniel Drake <drake@endlessm.com>, Joe Perches <joe@perches.com>,
	Johan Hovold <johan@kernel.org>,
	Richard Leitner <richard.leitner@skidata.com>,
	<linux-kernel@vger.kernel.org>,  <groeck@chromium.org>
Subject: Re: [PATCH] usb: hub: Per-port setting to use old enumeration scheme
Date: Wed, 23 May 2018 10:03:55 -0400 (EDT)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.1805230958590.1481-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20180523021656.122455-1-drinkcat@chromium.org>

On Wed, 23 May 2018, Nicolas Boichat wrote:

> The "old" enumeration scheme is considerably faster (it takes
> ~294ms instead of ~439ms to get the descriptor).
> 
> It is currently only possible to use the old scheme globally
> (/sys/module/usbcore/parameters/old_scheme_first), which is not
> desirable as the new scheme was introduced to increase compatibility
> with more devices.
> 
> However, in our case, we care about time-to-active for a specific
> USB device (which we make the firmware for), on a specific port
> (that is pogo-pin based: not a standard USB port). This new
> sysfs option makes it possible to use the old scheme on a single
> port only.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> ---
> 
> There are other "quirks" that we could add to reduce further
> enumeration time (e.g. reduce USB debounce time, reduce TRSTRCY
> to 10ms instead of 50ms as used currently), but the logic is quite
> similar, so it'd be good to have this reviewed first.

I'm not opposed to the idea in principle, although I don't like your
implementation because it breaks the original old_scheme_first
parameter.

Let's see what some other people think.

Yours is a rather special case, because you know exactly what device
will be attached to a specific port.  Still, I can see that sort of
thing happening in constrained and special-purpose settings.

How do you arrange to set the new quirk before the device is 
discovered?

Alan Stern

WARNING: multiple messages have this Message-ID (diff)
From: Alan Stern <stern@rowland.harvard.edu>
To: Nicolas Boichat <drinkcat@chromium.org>
Cc: linux-usb@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Felipe Balbi <felipe.balbi@linux.intel.com>,
	Eugene Korenevsky <ekorenevsky@gmail.com>,
	Peter Chen <peter.chen@nxp.com>,
	Daniel Drake <drake@endlessm.com>, Joe Perches <joe@perches.com>,
	Johan Hovold <johan@kernel.org>,
	Richard Leitner <richard.leitner@skidata.com>,
	linux-kernel@vger.kernel.org, groeck@chromium.org
Subject: usb: hub: Per-port setting to use old enumeration scheme
Date: Wed, 23 May 2018 10:03:55 -0400 (EDT)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.1805230958590.1481-100000@iolanthe.rowland.org> (raw)

On Wed, 23 May 2018, Nicolas Boichat wrote:

> The "old" enumeration scheme is considerably faster (it takes
> ~294ms instead of ~439ms to get the descriptor).
> 
> It is currently only possible to use the old scheme globally
> (/sys/module/usbcore/parameters/old_scheme_first), which is not
> desirable as the new scheme was introduced to increase compatibility
> with more devices.
> 
> However, in our case, we care about time-to-active for a specific
> USB device (which we make the firmware for), on a specific port
> (that is pogo-pin based: not a standard USB port). This new
> sysfs option makes it possible to use the old scheme on a single
> port only.
> 
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> ---
> 
> There are other "quirks" that we could add to reduce further
> enumeration time (e.g. reduce USB debounce time, reduce TRSTRCY
> to 10ms instead of 50ms as used currently), but the logic is quite
> similar, so it'd be good to have this reviewed first.

I'm not opposed to the idea in principle, although I don't like your
implementation because it breaks the original old_scheme_first
parameter.

Let's see what some other people think.

Yours is a rather special case, because you know exactly what device
will be attached to a specific port.  Still, I can see that sort of
thing happening in constrained and special-purpose settings.

How do you arrange to set the new quirk before the device is 
discovered?

Alan Stern
---
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  reply	other threads:[~2018-05-23 14:03 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-23  2:16 [PATCH] usb: hub: Per-port setting to use old enumeration scheme Nicolas Boichat
2018-05-23  2:16 ` Nicolas Boichat
2018-05-23 14:03 ` Alan Stern [this message]
2018-05-23 14:03   ` Alan Stern
2018-05-23 16:39   ` [PATCH] " Greg Kroah-Hartman
2018-05-23 16:39     ` Greg Kroah-Hartman
2018-05-23 23:42     ` [PATCH] " Nicolas Boichat
2018-05-23 23:42       ` Nicolas Boichat
2018-05-24 14:29       ` [PATCH] " Alan Stern
2018-05-24 14:29         ` Alan Stern
2018-05-24 16:21       ` [PATCH] " Greg Kroah-Hartman
2018-05-24 16:21         ` Greg Kroah-Hartman
2018-05-24 22:05         ` [PATCH] " Nicolas Boichat
2018-05-24 22:05           ` Nicolas Boichat
2018-05-25  6:29           ` [PATCH] " Greg Kroah-Hartman
2018-05-25  6:29             ` Greg Kroah-Hartman
2018-05-25  6:30 ` [PATCH] " Greg Kroah-Hartman
2018-05-25  6:30   ` Greg Kroah-Hartman

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