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Mon, 31 Aug 2026 08:23:56 -0700 (PDT) Date: Mon, 31 Aug 2026 17:23:54 +0200 From: Petr Mladek To: Sebastian Andrzej Siewior Cc: John Ogness , Greg Kroah-Hartman , Jiri Slaby , Andy Shevchenko , Jon Hunter , Thierry Reding , linux-kernel@vger.kernel.org, Ilpo =?iso-8859-1?Q?J=E4rvinen?= , Andy Shevchenko , Crescent Hsieh , Hugo Villeneuve , linux-serial@vger.kernel.org Subject: Re: [PATCH tty 1/1] serial: 8250: Change console_msr_work to IRQ_WORK_LAZY Message-ID: References: <20260828155811.270462-1-john.ogness@linutronix.de> <20260828155811.270462-2-john.ogness@linutronix.de> <20260828160652.TQBsi8oO@linutronix.de> Precedence: bulk X-Mailing-List: linux-serial@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: <20260828160652.TQBsi8oO@linutronix.de> On Fri 2026-08-28 18:06:52, Sebastian Andrzej Siewior wrote: > On 2026-08-28 18:04:08 [+0206], John Ogness wrote: > > For some platforms it is a problem to queue irq_work when entering > > cpuidle states. Since irq_work is used for deferred MSR handling, > > any atomic console printing when entering cpuidle states can lead > > to the affected hardware hanging. Tegra20 and Tegra30 are examples > > of such platforms. Avoiding raising the irq_work IRQ has shown to > > circumvent the problem. > > > Change the console_msr_work to be IRQ_WORK_LAZY, thus not raising > > an IRQ upon irq_work queuing. The irq_work is then handled on the > > next interrupt (worst case, kernel tick). > > Not on the next interrupt, on the next jiffies tick. Should you run > tickless and should the CPU have the tick switch off then it will raise > the irq-work interrupt anyway. This seems to be more precise. There is one more scenario. It would run in a dedicated kthread with PREEMPT_RT. I hope that nobody would run tickless system on the old Tegra hardware. So, this change should be good enough in reality. Anyway, I would prefer to get this "workaround" in for 7.3. In each case, I would not want to revert the uart 8250 conversion to nbcon because it did break the Tegra hardware. Best Regards, Petr