linux-kernel - Re: [PATCH 3/5] CHROMIUM: usb: dwc2: Avoid double-reset at boot time

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Date:	Thu, 8 Oct 2015 10:34:49 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	John Youn <John.Youn@...opsys.com>
Cc:	Yunzhi Li <lyz@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Julius Werner <jwerner@...omium.org>,
	Douglas Anderson <dianders@...omium.org>,
	John Youn <johnyoun@...opsys.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] CHROMIUM: usb: dwc2: Avoid double-reset at boot time

Hi,

On Wed, Oct 7, 2015 at 5:48 PM, Douglas Anderson <dianders@...omium.org> wrote:
> In (usb: dwc2: reset dwc2 core before dwc2_get_hwparams()) we added an
> extra reset to the probe path for the dwc2 USB controllers.  This
> allowed proper detection of parameters even if the firmware had already
> used the USB part.
>
> Unfortunately, this extra reset is quite slow and is affecting boot
> speed.  We can avoid the double-reset by skipping the extra reset that
> would happen just after the one we added.  Logic that explains why this
> is safe:
>
> * As of the CL mentioned above, we now always call dwc2_core_reset() in
>   dwc2_driver_probe() before dwc2_hcd_init().
>
> * The only caller of dwc2_hcd_init() is dwc2_driver_probe(), so we're
>   guaranteed that dwc2_core_reset() was called before dwc2_hdc_init().
>
> * dwc2_hdc_init() is the only caller that passes an irq other than -1 to
>   dwc2_core_init().  Thus if dwc2_core_init() is called with an irq
>   other than -1 we're guaranteed that dwc2_core_reset was called before
>   dwc2_core_init().
>
> ...this allows us to remove the dwc2_core_reset() in dwc2_core_init() if
> irq is not < 0.
>
> Note that since "irq" wasn't used in the function dwc2_core_init()
> anyway and since select_phy was always set at exactly the same times we
> could avoid the reset, we remove "irq" and rename "select_phy" to
> "initial_setup" and adjust the callers accordingly.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>  drivers/usb/dwc2/core.c | 29 ++++++++++++++++++-----------
>  drivers/usb/dwc2/core.h |  2 +-
>  drivers/usb/dwc2/hcd.c  |  6 +++---
>  3 files changed, 22 insertions(+), 15 deletions(-)

Obviously I stupidly forgot to remove the "CHROMIUM" prefix on this
patch.  :(  Sorry about that.  I can repost if necessary...

-Doug
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