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Wed, 01 Jul 2020 22:40:37 -0700 (PDT) From: Sergey Senozhatsky X-Google-Original-From: Sergey Senozhatsky Date: Thu, 2 Jul 2020 14:40:33 +0900 To: Tony Lindgren Cc: Petr Mladek , Andy Shevchenko , Raul Rangel , Sergey Senozhatsky , linux-kernel , Greg Kroah-Hartman , Andy Shevchenko , kurt@linutronix.de, "S, Shirish" , Peter Zijlstra , John Ogness , Steven Rostedt , Sergey Senozhatsky Subject: Re: UART/TTY console deadlock Message-ID: <20200702054033.GC3450@jagdpanzerIV.localdomain> References: <20200630035816.GA21591@jagdpanzerIV.localdomain> <20200630102141.GA11587@alley> <20200630105512.GA530@jagdpanzerIV.localdomain> <20200630122239.GD6173@alley> <20200630130534.GB145027@jagdpanzerIV.localdomain> <20200630180255.GD37466@atomide.com> <20200702051213.GB3450@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200702051213.GB3450@jagdpanzerIV.localdomain> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (20/07/02 14:12), Sergey Senozhatsky wrote: > Date: Thu, 2 Jul 2020 14:12:13 +0900 > From: Sergey Senozhatsky > To: Tony Lindgren > Cc: Sergey Senozhatsky , Petr Mladek > , Andy Shevchenko , Raul > Rangel , Sergey Senozhatsky > , linux-kernel > , Greg Kroah-Hartman > , Andy Shevchenko > , kurt@linutronix.de, "S, Shirish" > , Peter Zijlstra , John Ogness > , Steven Rostedt > Subject: Re: UART/TTY console deadlock > Message-ID: <20200702051213.GB3450@jagdpanzerIV.localdomain> > > On (20/06/30 11:02), Tony Lindgren wrote: > > This conditional disable for irq_shared does not look nice to me > > from the other device point of view :) > > > > Would it be possible to just set up te dummy interrupt handler > > for the startup, then change it back afterwards? See for example > > omap8250_no_handle_irq(). > > I think we can do it. serial8250_do_startup() and irq handler take > port->lock, so they should be synchronized. Hmm, hold on. Why does it disable IRQ in the first place? IRQ handlers should grab the port->lock. So if there is already running IRQ, then serial8250_do_startup() will wait until IRQ handler unlocks the port->lock. If serial8250_do_startup() grabs the port->lock first, then IRQ will wait for serial8250_do_startup() to unlock it. serial8250_do_startup() does not release the port->unlock until its done: spin_lock_irqsave(&port->lock, flags); wait_for_xmitr(up, UART_LSR_THRE); serial_port_out_sync(port, UART_IER, UART_IER_THRI); udelay(1); /* allow THRE to set */ iir1 = serial_port_in(port, UART_IIR); serial_port_out(port, UART_IER, 0); serial_port_out_sync(port, UART_IER, UART_IER_THRI); udelay(1); /* allow a working UART time to re-assert THRE */ iir = serial_port_in(port, UART_IIR); serial_port_out(port, UART_IER, 0); spin_unlock_irqrestore(&port->lock, flags); so IRQ will not see the inconsistent device state. What exactly is the purpose of disable_irq_nosync()? Can we just remove disable_irq_nosync()/enable_irq() instead? Are there any IRQ handlers that don't acquire the port->lock? -ss