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Peter Anvin" , x86@kernel.org, Jonathan Corbet , Catalin Marinas , Will Deacon , Timur Tabi , graeme.gregory@linaro.org, mark.salter@redhat.com From: Prarit Bhargava Message-ID: <03e799c6-a0f3-eccf-882d-78205e9335ad@redhat.com> Date: Mon, 12 Feb 2018 10:18:06 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <20180212145652.GM25181@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-serial-owner@vger.kernel.org X-Mailing-List: linux-serial@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On 02/12/2018 09:56 AM, Peter Zijlstra wrote: > On Mon, Feb 12, 2018 at 08:47:57AM -0500, Prarit Bhargava wrote: >> >> >> On 02/12/2018 08:34 AM, Peter Zijlstra wrote: >>> On Thu, Jan 18, 2018 at 10:09:51AM -0500, Prarit Bhargava wrote: >>>> config ACPI_SPCR_TABLE >>>> + bool "ACPI Serial Port Console Redirection Support" >>>> + default y if X86 >>>> + help >>>> + Enable support for Serial Port Console Redirection (SPCR) Table. >>>> + This table provides information about the configuration of the >>>> + earlycon console. >>> >>> I just got asked this by oldconfig, which left me rather puzzled, WTF >>> does this do? >> >> Odd -- I thought I had taken care of that :( My apologies Peter. >> >> ACPI SPCR is used by a vendor to define the serial console for a system. If >> SPCR exists a user can add kernel parameter "earlycon" (no extra kernel >> parameters) and the console will work out-of-the-box. >> >> The serial console configuration varies from vendor to vendor. This takes the >> guess-work out of defining a serial console. > > But when I specify "earlyprintk=serial,ttyS0,115200" this SPCR crud will > not interfere? > I tested "earlyprintk=serial,ttyS0,115200" on a system which is known to have a functional console with "console=ttyS0,1152008N1" both with and without CONFIG_ACPI_SPCR_TABLE enabled. I do not see any significant difference in output. diff of boot logs: --- earlyprintk_no_spcr_enable 2018-02-12 10:11:00.477288423 -0500 +++ earlyprintk_spcr_enable 2018-02-12 10:16:02.282574797 -0500 @@ -1,5 +1,5 @@ microcode: microcode updated early to revision 0x2000035, date = 2017-10-17 -Linux version 4.15.0+ (root@intel-purley-lr-02.khw.lab.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-28) (GCC)) #5 SMP Mon Feb 12 10:06:08 EST 2018 +Linux version 4.15.0+ (root@intel-purley-lr-02.khw.lab.eng.bos.redhat.com) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-28) (GCC)) #6 SMP Mon Feb 12 10:11:42 EST 2018 Command line: BOOT_IMAGE=/vmlinuz-4.15.0+ root=/dev/mapper/rhel_intel--purley--lr--02-root ro crashkernel=auto rd.lvm.lv=rhel_intel-purley-lr-02/root rd.lvm.lv=rhel_intel-purley-lr-02/swap earlyprintk=serial,ttyS0,115200 LANG=en_US.UTF-8 x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers' x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers' @@ -205,7 +205,7 @@ e820: last_pfn = 0x6f800 max_arch_pfn = 0x400000000 Using GB pages for direct mapping Secure boot disabled -RAMDISK: [mem 0x3a563000-0x3bba2fff] +RAMDISK: [mem 0x3a5da000-0x3bba2fff] ACPI: Early table checksum verification disabled ACPI: RSDP 0x000000006922A014 000024 (v02 INTEL ) ACPI: XSDT 0x00000000690DD188 000114 (v01 INTEL EDK2 00000000 01000013) @@ -519,6 +519,8 @@ ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level) Using ACPI (MADT) for SMP configuration information ACPI: HPET id: 0x8086a701 base: 0xfed00000 +ACPI: SPCR: SPCR table version 1 +ACPI: SPCR: console: uart,io,0x3f8,115200 smpboot: Allowing 432 CPUs, 224 hotplug CPUs PM: Registered nosave memory: [mem 0x00000000-0x00000fff] PM: Registered nosave memory: [mem 0x000a0000-0x000fffff] @@ -555,10 +557,10 @@ log_buf_len total cpu_extra contributions: 1765376 bytes log_buf_len min size: 524288 bytes log_buf_len: 4194304 bytes -early log buf free: 477984(91%) -Memory: 394593504K/401282564K available (10252K kernel code, 2147K rwdata, 3664K rodata, 2504K init, 1800K bss, 6689060K reserved, 0K cma-reserved) +early log buf free: 477876(91%) +Memory: 394593976K/401282564K available (10252K kernel code, 2147K rwdata, 3664K rodata, 2504K init, 1800K bss, 6688588K reserved, 0K cma-reserved) Kernel/User page tables isolation: enabled -ftrace: allocating 35205 entries in 138 pages +ftrace: allocating 35206 entries in 138 pages Hierarchical RCU implementation. RCU restricting CPUs from NR_CPUS=8192 to nr_cpu_ids=432. Tasks RCU enabled. P.