linux-kernel - Re: [PATCH tty-next v1 1/4] serial: 8250: Use @ier bits to determine if Rx is stopped

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Message-ID: <Z2COCeWqyauMYYyk@smile.fi.intel.com>
Date: Mon, 16 Dec 2024 22:31:05 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Esben Haabendal <esben@...nix.com>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Rengarajan S <rengarajan.s@...rochip.com>,
	Bart Van Assche <bvanassche@....org>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Serge Semin <fancer.lancer@...il.com>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH tty-next v1 1/4] serial: 8250: Use @ier bits to determine
 if Rx is stopped

On Mon, Dec 16, 2024 at 06:18:41PM +0106, John Ogness wrote:
> Commit f19c3f6c8109 ("serial: 8250_port: Don't service RX FIFO if
> throttled") uses @read_status_mask (bit UART_LSR_DR) to determine
> if Rx has been stopped. However, the bit UART_LSR_DR is not
> managed properly in @read_status_mask for all Rx stop/start
> situations and is therefore not suitable for this purpose.
> 
> Use the UART_IER_RLSI and UART_IER_RDI bits in @ier instead, as
> this is already common in 8250-variants and drivers.

Hmm... IER is Interrupt Enable Register, so it has been programmed to the value
we control, on the opposite the LSR is Line Status Register and defines status
on the line at the moment of reading. Can you elaborate how your change is correct
substitute?

-- 
With Best Regards,
Andy Shevchenko