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s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=QaCEMyw673l1y1m9Q75tzdHJjzrSk1MCLu8X7K/518o=; b=PeAsHBFMHaXAV/ALGdosYCJO26EklWw1SMOtdKj0lMV3I1oHvvWJSodY9fdVehtHAb cUam/A7KTTtHztvWs1mPCKuLOs/c6HLs4OVkEoSuU5/DxI3zzRFFDRYsys12vNskNTXV 3m+Tq2CZ14WqEw/vQ6nfY29iGa1XuM5qkYrlxxNYOE4YEwQ3Qgf/nr7kDuT/iSoOnemN Zs73RVclfHgTc9CX/vOD/m1+bNlKwjPDNbOIArCqVu2xWGA5OoaaEFqjGiDgT94qyyjP 5Wg7+zLugW9QznE/MxXYO2GCWKODQ9pOV/HFrSkGBdBv1DUX4UZT6k0OeMQYvyWFFIIJ k0mQ== X-Gm-Message-State: AOAM532GO8BVaU+M5okFqJgktezZcBIhEgAJ3ZaX6ReByUkX//+y+7TC qjZFHxV8733bkojP+QI3tGdhDxKnizNVG47W0RE= X-Google-Smtp-Source: ABdhPJy32iCy6XBozpoT9fuebNVSm/nAnAmObrf6L1/8ic+Q2Gqd26pkP2y55Wj7jrTCvejqoLnFYdeR1BLyRbWDiTM= X-Received: by 2002:a05:6402:2076:: with SMTP id bd22mr2326007edb.378.1614711797814; Tue, 02 Mar 2021 11:03:17 -0800 (PST) MIME-Version: 1.0 References: <20210120144454.f6b72lnasw4q3bde@fsr-ub1664-175> <20210120151305.GC19063@pengutronix.de> <20210120152813.x2pbs5vprevkly23@fsr-ub1664-175> <20210120155001.GD19063@pengutronix.de> <20210120161421.h3yng57m3fetwwih@fsr-ub1664-175> <20210121095617.GI19063@pengutronix.de> <20210121102450.lisl3mzqczdsmzda@fsr-ub1664-175> <20210215130620.3la4bexamozzcvjx@fsr-ub1664-175> In-Reply-To: <20210215130620.3la4bexamozzcvjx@fsr-ub1664-175> From: Adam Ford Date: Tue, 2 Mar 2021 13:03:04 -0600 Message-ID: Subject: Re: [PATCH V3] clk: imx: Fix reparenting of UARTs not associated with sdout To: Abel Vesa Cc: Sascha Hauer , arm-soc , Adam Ford-BE , Aisheng Dong , Michael Turquette , Stephen Boyd , Shawn Guo , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , Linus Walleij , Jerome Brunet , linux-clk , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 15, 2021 at 7:06 AM Abel Vesa wrote: > > On 21-02-13 08:44:28, Adam Ford wrote: > > On Wed, Feb 3, 2021 at 3:22 PM Adam Ford wrote: > > > > > > On Thu, Jan 21, 2021 at 4:24 AM Abel Vesa wrote: > > > > > > > > On 21-01-21 10:56:17, Sascha Hauer wrote: > > > > > On Wed, Jan 20, 2021 at 06:14:21PM +0200, Abel Vesa wrote: > > > > > > On 21-01-20 16:50:01, Sascha Hauer wrote: > > > > > > > On Wed, Jan 20, 2021 at 05:28:13PM +0200, Abel Vesa wrote: > > > > > > > > On 21-01-20 16:13:05, Sascha Hauer wrote: > > > > > > > > > Hi Abel, > > > > > > > > > > > > > > > > > > On Wed, Jan 20, 2021 at 04:44:54PM +0200, Abel Vesa wrote= : > > > > > > > > > > On 21-01-18 08:00:43, Adam Ford wrote: > > > > > > > > > > > On Mon, Jan 18, 2021 at 6:52 AM Abel Vesa wrote: > > > > > > > > > > > > > > > > ... > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > TBH, I'm against the idea of having to call consume= r API from a clock provider driver. > > > > > > > > > > > > I'm still investigating a way of moving the uart cl= ock control calls in drivers/serial/imx, > > > > > > > > > > > > where they belong. > > > > > > > > > > > > > > > > > > > > > > That makes sense. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Just a thought. The uart clock used for console remains= on from u-boot, > > > > > > > > > > so maybe it's enough to just add the CLK_IGNORE_UNUSED = flag to all the > > > > > > > > > > uart root clocks and remove the prepare/enable calls fo= r uart clocks > > > > > > > > > > for good. I don't really have a way to test it right no= w, but maybe > > > > > > > > > > you could give it a try. > > > > > > > > > > > > > > > > > > That would mean that UART clocks will never be disabled, = regardless of > > > > > > > > > whether they are used for console or not. That doesn't so= und very > > > > > > > > > appealing. > > > > > > > > > > > > > > > > AFAIK, the only uart clock that is enabled by u-boot is the= one used for > > > > > > > > the console. Later on, when the serial driver probes, it wi= ll enable it itself. > > > > > > > > > > > > > > > > Unless I'm missing something, this is exactly what we need. > > > > > > > > > > > > > > It might enable it, but with CLK_IGNORE_UNUSED the clock won'= t be > > > > > > > disabled again when a port is closed after usage > > > > > > > > > > > > OK, tell me what I'm getting wrong in the following scenario: > > > > > > > > > > > > U-boot leaves the console uart clock enabled. All the other one= s are disabled. > > > > > > > > > > > > Kernel i.MX clk driver registers the uart clocks with flag CLK_= IGNORE_UNUSED. > > > > > > > > > > I was wrong at that point. I originally thought the kernel will n= ever > > > > > disable these clocks, but in fact it only leaves them enabled dur= ing the > > > > > clk_disable_unused call. > > > > > > > > > > However, when CLK_IGNORE_UNUSED becomes relevant it's too late al= ready. > > > > > I just chatted with Lucas and he told me what the original proble= m was > > > > > that his patch solved. > > > > > > > > > > The problem comes when an unrelated device and the earlycon UART = have > > > > > the same parent clocks. The parent clock is enabled, but it's ref= erence > > > > > count is zero. Now when the unrelated device probes and toggles i= ts > > > > > clocks then the shared parent clock will be disabled due to the > > > > > reference count being zero. Next time earlycon prints a character= the > > > > > system hangs because the UART gates are still enabled, but their = parent > > > > > clocks no longer are. > > > > > > > > > > > > > Hmm, that is indeed a problem. That's why I think there should be s= ome > > > > kind of NOCACHE flag for almost all the types of clocks. For exampl= e, > > > > in this case, it makes sense for the core to check the bit in the r= egister > > > > and then disable the parent based on that instead of relying on the= refcount. > > > > Anyway, that's something that needs to be added in the CCF. > > > > > > > > > Overall I think Lucas' patches are still valid and relevant and w= ith > > > > > Adams patches we even no longer have to enable all UART clocks, b= ut > > > > > only the ones which are actually needed. > > > > > > > > Yeah, for now, I think we can go with Adam's patches. But longterm,= I would > > > > like to remove the special case of the uart clocks we have right no= w in all > > > > the i.MX clock drivers. > > > > I looked around at other serial drivers, and I found nothing like this > > function for enabling all UART clocks. There are generic functions > > for registering consoles, earlycon etc, and the serial driver fetches > > the per and igp clocks from the device tree, so I attempted to simply > > remove imx_register_uart_clocks(). I booted an i.MX8M Nano from a > > fully-powered off state, and my serial console came up just fine. > > Just because it works, doesn't mean it is safe. To put it simply, the > risk of some driver disabling a clock that is parent of the uart clock > would render the earlycon broken. > > > > > I checked the clk_summary, and the clock parents are set correctly and > > the respective clock rates appear to be correct (ie, the console is > > working at the desired baud rate, and Bluetooth is happy) > > > > Since I don't fully understand the serial driver and the clock > > dependencies, I don't want to just simply remove the function without > > discussing it, because I don't know the ramifications. However, when > > testing on the i.MX8M Nano, things look OK. > > I also tested suspend-resume and the console UART appears to return > > and the Bluetooth UART set to 4Mbps works just fine too. > > > > I'd like to post a V4 which just removes imx_register_uart_clocks and > > the corresponding calls to it. I don't know enough about the older > > 32-bit i.MX SoC's, but I have build-tested it, and I can generate a > > patch. Are there any objections and/or concerns? > > > > Please don't remove the imx_register_uart_clocks for now. As much as I > would like it gone, the way the earlycon could end up broken is > so ugly that it would make it a real pain to debug it later on. I won't do a V4, but where do we go from here? I have a V3 that was waiting for reviews, but there were some concerns. We currently cannot re-parent the UART's on iMX8MM or iMX8MN. Should I resend V3, or are there fixes/changes requested to V3? adam > > > adam > > > > > > > > > > Is the patch I submitted good enough for someone's acked-by or > > > reviewed-by, or are there changes I need to implement? > > > > > > adam > > > > > > > > > > > > > Sascha > > > > > > > > > > > > > > > -- > > > > > Pengutronix e.K. | = | > > > > > Steuerwalder Str. 21 | https://eur01.safeli= nks.protection.outlook.com/?url=3Dhttp%3A%2F%2Fwww.pengutronix.de%2F&da= ta=3D04%7C01%7Cabel.vesa%40nxp.com%7C12862aeac2934a4a94f108d8d02de573%7C686= ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637488242849833051%7CUnknown%7CTWFp= bGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%= 7C1000&sdata=3DfKDvWYJIU7hBROH6yDM9FYUCHJDK9wMjTeJDMxRff8o%3D&reser= ved=3D0 | > > > > > 31137 Hildesheim, Germany | Phone: +49-5121-2069= 17-0 | > > > > > Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-2069= 17-5555 |