From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC8323E58CD for ; Mon, 5 May 2025 23:34:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746488045; cv=none; b=F31W6eJ8mS2gMnkhnQqIBDKPwUKQsqz0In/lW2xcRND2KQVMzFokscQWklYG3ZD28WrvkawCfb54sI8mtB4+//4ztAKJ/OEALJFjnZjvRb8hZtO0UgzC777l6t9kqIv3a1E6fEeTxKZIzwnjLPDSps/r6J0sAtmCjps+zkns6qE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746488045; c=relaxed/simple; bh=sve3vY3CJA2H9KhL6N14xJagE0byGd/9BYCCTSFziCU=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=uJSLi2cWNwI+54U87cG1T/7jyGE1vXSB93rzFI1AM45qpZydqqCCa1GEfawooBXSGtdT/oqbC/MSL/v/XjBraNb4cfnuir5YExTapJZQDT2DELoCObo8RVL8740c0cAFLZseuGb3eVFx/5FHJAk5hoyVJSPqT923JMTfc/Aqvdo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=FSBQfC35; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="FSBQfC35" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=uiR+3CEeBKWRWtRm+179P73pOavCkS1oCUl8AfS/Uy8=; b=FSBQfC35lzQuk08eQZwxVcd1Fz jaT+Xw4o0DNf/FLkrmbiNM+IAtdZZQ0AeKURjSPGYJZcjMbZe+BY3CV4llkKc7uUU/ZC0aukncCXq hEap0BvotUz46fMgw6/NpMfB1ue1Zdyd6GD1lRi7Wk6NnxIIKqaNwdHNk7uGGfO5Ka6BG2ilIv6xb hENt1sb73US3e3dtiMvodMXwkwyXh+A3btgQOv+2oWlnj1B4RF30+jp90dnezZ1uivM37f0otSm1P Xf6kVzcJXKw19mYGsm0YOZ3iSRX9SVkulTVDT0fFReBlHDPzM5VEGgLmKRJDjNC+LZ0e16CX6qNNC OKCdK0DQ==; Received: from [15.248.7.87] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1uC5Ij-0000000FZLN-0KnB; Mon, 05 May 2025 23:33:53 +0000 Message-ID: <944ddefdc0ef3dc0f78c7957afa7f12e360a4392.camel@infradead.org> Subject: Re: [PATCH v1 0/6] x86/boot: Enable earlyprintk on MMIO (8-bit) From: David Woodhouse To: Andy Shevchenko Cc: Ashish Kalra , "Kirill A. Shutemov" , linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Denis Mukhin Date: Mon, 05 May 2025 16:32:38 -0700 In-Reply-To: References: <20250502123145.4066635-1-andriy.shevchenko@linux.intel.com> <3c1bd53c8ee5fe0a6e281551dfe2089679e8e5eb.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-1hyg0VtQQ3LT5b4SyEmR" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-1hyg0VtQQ3LT5b4SyEmR Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2025-05-05 at 18:01 +0300, Andy Shevchenko wrote: > On Mon, May 05, 2025 at 05:59:48PM +0300, Andy Shevchenko wrote: > > On Mon, May 05, 2025 at 07:35:04AM -0700, David Woodhouse wrote: > > > On Mon, 2025-05-05 at 17:05 +0300, Andy Shevchenko wrote: > > > > On Fri, May 02, 2025 at 10:33:49AM -0700, David Woodhouse > > > > wrote: > > > > > On Fri, 2025-05-02 at 15:29 +0300, Andy Shevchenko wrote: > > > > > > Some of the platforms may have no legacy COM ports and only > > > > > > provide > > > > > > an MMIO accessible UART. Add support for such to > > > > > > earlyprintk for the > > > > > > boot phase of the kernel. > > > > >=20 > > > > > Shiny. I had to hack QEMU's PCI serial port to do unnatural > > > > > things, in > > > > > order to test the mmio32 variant which was the only thing the > > > > > earlyprintk code used to support. But I *did* so, and it > > > > > works with the > > > > > kexec debugging. > > > > >=20 > > > > > Can you add support for this mode to the kexec debugging too, > > > > > please? > > > >=20 > > > > Do you mean to add MMIO 8-bit to kexec assembly code and other > > > > parts like you > > > > did in the below mentioned change? > > > >=20 > > > > I can try it at some point, but have no time right now for > > > > this. > > > > I would appreciate if you can give a try for this patch series > > > > functionality to see if it helps for the initial messages (as > > > > far as I understand you also want to have this in the second > > > > kernel, right?). > > >=20 > > > I'll see if I can find the time to take a look. Got a branch I > > > can pull > > > your series from? > >=20 > > Yeo, > > https://bitbucket.org/andy-shev/linux/commits/branch/topic%2Fx86%2Fboot= -earlyprintk > > . >=20 > But just FYI that with `b4` it's as easy to pull from the mailing > list as from > a branch: >=20 > b4 am > 20250502123145.4066635-1-andriy.shevchenko@linux.intel.com > git am -C1 -s ... Thanks. Should I be expecting this to work...? qemu-system-x86_64 -display none -vga none -accel kvm,kernel-irqchip=3Dspl= it \ -kernel arch/x86/boot/bzImage \ -append "console=3DttyS4 root=3D/dev/vda1 earlyprintk=3Dpciserial" \ -chardev stdio,mux=3Don,id=3Dchar0,signal=3Doff -mon char0 -device pci-se= rial,chardev=3Dchar0 I get no early output (I think it's still using the mmio32 variant), and I only see output from when the real driver takes over: [ 0.894054] printk: legacy console [ttyS4] enabled [ 0.895498] printk: legacy bootconsole [earlyser0] disabled ... --=-1hyg0VtQQ3LT5b4SyEmR Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi 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