From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH 4/7] phy: meson: add USB2 PHY support for Meson8b and GXBB Date: Mon, 12 Sep 2016 10:32:44 -0700 Message-ID: <7hpoo9qb0j.fsf@baylibre.com> References: <20160904213152.25837-1-martin.blumenstingl@googlemail.com> <20160904213152.25837-5-martin.blumenstingl@googlemail.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: (Martin Blumenstingl's message of "Sun, 11 Sep 2016 15:44:03 +0200") Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Martin Blumenstingl Cc: p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org, hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Ben Dooks , mark.rutland-5wv7dgnIgG8@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, johnyoun-HKixBCOQz3hWk0Htik3J/w@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, mturquette-rdvid1DuHRBWk0Htik3J/w@public.gmane.org, linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org, kishon-l0cyMroinI0@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, catalin.marinas-5wv7dgnIgG8@public.gmane.org, carlo-KA+7E9HrN00dnm+yROfE0A@public.gmane.org, linux-amlogic-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, jbrunet-rdvid1DuHRBWk0Htik3J/w@public.gmane.org List-Id: devicetree@vger.kernel.org Martin Blumenstingl writes: > On Fri, Sep 9, 2016 at 10:36 PM, Martin Blumenstingl > wrote: >> On Fri, Sep 9, 2016 at 5:33 PM, Kevin Hilman wrote: >>> Martin Blumenstingl writes: >>> >>>> On Thu, Sep 8, 2016 at 10:53 PM, Ben Dooks wrote: >>>>> On 08/09/16 21:42, Kevin Hilman wrote: >>>>>> >>>>>> Ben Dooks writes: >>>>>> >>>>>>> On 08/09/16 20:52, Martin Blumenstingl wrote: >>>>>>>> >>>>>>>> On Thu, Sep 8, 2016 at 9:35 PM, Kevin Hilman >>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>> + phy = devm_phy_create(&pdev->dev, NULL, &phy_meson_usb2_ops); >>>>>>>>>> + if (IS_ERR(phy)) { >>>>>>>>>> + dev_err(&pdev->dev, "failed to create PHY\n"); >>>>>>>>>> + return PTR_ERR(phy); >>>>>>>>>> + } >>>>>>>>>> + >>>>>>>>>> + if (usb_reset_refcnt++ == 0) { >>>>>>>>>> + ret = device_reset(&pdev->dev); >>>>>>>>>> + if (ret) { >>>>>>>>>> + dev_err(&phy->dev, "Failed to reset USB PHY\n"); >>>>>>>>>> + return ret; >>>>>>>>>> + } >>>>>>>>>> + } >>>>>>>>> >>>>>>>>> >>>>>>>>> The ref count + reset here looks like something that could/should be >>>>>>>>> handled in a runtime PM callback. >>>>>>>> >>>>>>>> Unfortunately that doesn't work (as Jerome found out) because both >>>>>>>> PHYs are sharing the same reset line. >>>>>>>> So if the second PHY would call device_reset then it would also reset >>>>>>>> the first PHY! >>>>>>>> >>>>>>>> There's a comment above the declaration of usb_reset_refcnt which >>>>>>>> tries to explain this: >>>>>>>> "The PHYs are sharing a common reset line -> we are only allowed to >>>>>>>> reset once for all PHYs." >>>>>>>> Maybe I should move this comment to the "if (usb_reset_refcnt++ == 0) >>>>>>>> {" line to make it easier to see? >>>>>>>> >>>>>>> >>>>>>> pm-runtime has refcounting in it. When one of the nodes turns on, >>>>>>> the pm-runtime will call your driver to say there is a user when >>>>>>> this first use turns up. >>>>>>> >>>>>>> If all the sub-phys turn off and drop their refcount then the driver >>>>>>> is called to say there are no more users and you can go to sleep. >>>>>> >>>>>> >>>>>> After a chat w/Martin on IRC, It turns out runtime PM wont help here. >>>>>> >>>>>> The reason is because there are physically two PHY devices[1]. Those 2 >>>>>> devices will be treated independely by runtime PM, and have separate >>>>>> use-counting, which means doing what I proposed would cause a reset to >>>>>> happen when either device was probed. >>>>>> >>>>>> So, I think it's OK as it is. >>>>> >>>>> >>>>> Surely you can do pm_runtime_get/put on the phy's parent platform >>>>> device and do it that way? >>>> could you please be more specific with that (do you mean pdev->dev.parent)? >>>> so we would use pm_runtime_{get_sync,put} with the parent, while we >>>> would still define the runtime_resume in our driver. >>> >>> You'd also need to do get/put on the children, but yes, that's what Ben >>> is suggesting. >>> >>> However, the problem with all of the solutions proposed (runtime PM ones >>> included) is that we're forcing a board-specific design issue (2 devices >>> sharing a reset line) into a driver that should not have any >>> board-specific assumptions in it. >>> >>> For example, if this driver is used on another platform where different >>> PHYs have different reset lines, then one of them (the unlucky one who >>> is not probed first) will never get reset. So any form of per-device >>> ref-counting is not a portable solution. >> indeed, so in simple words we would need something like >> reset_control_do_once(rstc, RESET/ASSERT/DEASSERT) which would >> remember internally if any action has already been executed: if not it >> does a _reset, _assert or _deassert and otherwise it does nothing. > for now I've implemented something less hacky: I made the reset > optional and only specified it for phy0. That's slightly better, but could misbehave if devices are probed/loaded in different order? But, that shouldn't be a blocker for the driver. > During Jerome's tests the reset was not needed, while on my board it's > required to bring both PHYs up. > Additionally the USB PHY reference driver does not have any reset > logic for newer SoCs (GXL), so making the reset optional doesn't sound > that bad to me. Agreed. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html