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Peter Anvin" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] x86/early_printk: add MMIO-based UARTs Message-ID: References: <20250324-earlyprintk-v3-1-aee7421dc469@ford.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo On Mon, Apr 07, 2025 at 11:04:42PM +0000, Denis Mukhin wrote: > On Monday, April 7th, 2025 at 9:38 AM, Andy Shevchenko wrote: > > On Mon, Mar 24, 2025 at 05:55:40PM -0700, Denis Mukhin wrote: > > > During the bring-up of an x86 board, the kernel was crashing before > > > reaching the platform's console driver because of a bug in the firmware, > > > leaving no trace of the boot progress. > > > > > > It was discovered that the only available method to debug the kernel > > > boot process was via the platform's MMIO-based UART, as the board lacked > > > an I/O port-based UART, PCI UART, or functional video output. > > > > > > Then it turned out that earlyprintk= does not have a knob to configure > > > the MMIO-mapped UART. > > > > > > Extend the early printk facility to support platform MMIO-based UARTs > > > on x86 systems, enabling debugging during the system bring-up phase. > > > > > > The command line syntax to enable platform MMIO-based UART is: > > > earlyprintk=mmio,membase[,{nocfg|baudrate}][,keep] > > > > > > Note, the change does not integrate MMIO-based UART support to: > > > arch/x86/boot/early_serial_console.c > > > > > > Also, update kernel parameters documentation with the new syntax and > > > add missing 'nocfg' setting to PCI serial cards description. > > > > Just for your information: Have you seen this rather old series of mine? > > > > https://bitbucket.org/andy-shev/linux/commits/branch/topic%2Fx86%2Fboot-earlyprintk > > This is a nice cleanup! > Thanks for sharing. > > Sorry, I haven't seen the series above, I had to write a patch (which was months ago). > It's just I could not post it on the mailing list until recently. No problem. Can you look at https://lore.kernel.org/r/20250407172214.792745-1-andriy.shevchenko@linux.intel.com ? I forgot to Cc you and that is an important fix. -- With Best Regards, Andy Shevchenko