From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Roese Date: Fri, 11 Mar 2016 11:13:13 +0100 Subject: [U-Boot] [PATCH 4/6] usb: usb_hub_power_on(): Use 100ms power-on delay instead of 1 sec (optionally) In-Reply-To: <56E1C711.3080204@redhat.com> References: <1457625012-1268-1-git-send-email-sr@denx.de> <1457625012-1268-5-git-send-email-sr@denx.de> <56E1C711.3080204@redhat.com> Message-ID: <56E29A39.6000802@denx.de> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Hans, On 10.03.2016 20:12, Hans de Goede wrote: > On 10-03-16 16:50, Stefan Roese wrote: >> In a system with a complex USB infrastrcture (many USB hubs), the >> power-on delay of mininimum 1 second for each USB hub results in a quite >> big USB scanning time. Many USB devices can deal with much lower >> power-on delays. In my test system, even 10ms seems to be enough >> for the USB device to get detected correctly. This patch now >> reduces the minimum 1 second delay to a minumum of 100ms instead. >> This results in a big USB scan time reduction: >> >> Here the numbers for my current board: >> >> Without this patch: >> starting USB... >> USB0: USB EHCI 1.00 >> scanning bus 0 for devices... 9 USB Device(s) found >> >> time: 10.822 seconds >> >> With this patch: >> starting USB... >> USB0: USB EHCI 1.00 >> scanning bus 0 for devices... 9 USB Device(s) found >> >> time: 6.319 seconds >> >> So ~4.5 seconds of USB scanning time reduction. >> >> I'm not really sure if this patch can be accepted in general as is. >> >> In patch 0d437bca [usb: hub: fix power good delay timing] by Stephen >> Warren, this delay was changes according to "Connect Timing ECN.pdf" >> to a total of 1 second plus the hub port's power good time. Now its >> changes back to 100ms which is a violation of this spec. But still, >> for most USB devices this 100ms is more than enough. So its a valid >> use-case to lower this time in special (perhaps static) USB >> environments. > > Actually that 1 second + poweron delay is why we had the 1 sec > delay in usb_hub_configure(), that is where we wait for a device > to show up. Note that we can already save a lot of time, by > first powering up all ports and then doing the 1 sec wait > and then checking all ports without needing to delay any further. > > Or even better: > > 1) turn on all ports > 2) do power-on-delay (either 2ms * bPwrOn2PwrGood from descriptor, or > 100ms which ever one is LARGER) > 3) set a timeout val 1 sec from now, loop over all ports and quit > the loop when either all ports are connected (we already skip the > per port delay in this connected case now), or when the 1 sec > expires. There is no reason for the 1 sec per port delay, > one sec + bPwrOn2PwrGood delay is enough for all ports One question here: Do we really need to do this power-on-delay in step 2) at all? Shouldn't it be sufficient to do the port scanning loop with a "2ms * bPwrOn2PwrGood + 1 sec" timeout instead? As I've done in the patch I've attached (which works just fine on my platform). Note that I will also dig into the parallelizing idea as well. I'm just trying to implement the timeout handling correctly first. Thanks, Stefan -------------- next part -------------- A non-text attachment was scrubbed... Name: 0001-usb-Change-power-on-scanning-timeout-handling.patch Type: text/x-diff Size: 2656 bytes Desc: not available URL: