linux-serial.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: "Heiko Stübner" <heiko@sntech.de>
To: Giulio Benetti <giulio.benetti@micronovasrl.com>
Cc: gregkh@linuxfoundation.org, jslaby@suse.com,
	andriy.shevchenko@linux.intel.com, matwey.kornilov@gmail.com,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
	lukas@wunner.de, christoph.muellner@theobroma-systems.com
Subject: Re: [PATCH v2 4/7] serial: 8250: Handle implementations not having TEMT interrupt using em485
Date: Sun, 17 May 2020 17:04:28 +0200	[thread overview]
Message-ID: <3036126.9QgpAzkLCg@diego> (raw)
In-Reply-To: <ac74f702-9444-f660-974b-85a006805070@micronovasrl.com>

Hi Giulio,

Am Donnerstag, 26. März 2020, 03:02:39 CEST schrieb Giulio Benetti:
> Il 26/03/2020 01:05, Heiko Stübner ha scritto:
> > Am Donnerstag, 26. März 2020, 00:47:38 CET schrieb Giulio Benetti:
> >> very cleaner way to handle TEMT as a capability!
> >> And I've found one thing...
> >>
> >> Il 26/03/2020 00:14, Heiko Stuebner ha scritto:
> >>> From: Giulio Benetti <giulio.benetti@micronovasrl.com>
> >>>
> >>> Some 8250 ports have a TEMT interrupt but it's not a part of the 8250
> >>> standard, instead only available on some implementations.
> >>>
> >>> The current em485 implementation does not work on ports without it.
> >>> The only chance to make it work is to loop-read on LSR register.
> >>>
> >>> So add UART_CAP_TEMT to mark 8250 uarts having this interrupt,
> >>> update all current em485 users with that capability and make
> >>> the stop_tx function loop-read on uarts not having it.
> >>>
> >>> Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
> >>> [moved to use added UART_CAP_TEMT, use readx_poll_timeout]
> >>> Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
> >>> ---
> >>>    drivers/tty/serial/8250/8250.h            |  1 +
> >>>    drivers/tty/serial/8250/8250_bcm2835aux.c |  2 +-
> >>>    drivers/tty/serial/8250/8250_of.c         |  2 ++
> >>>    drivers/tty/serial/8250/8250_omap.c       |  2 +-
> >>>    drivers/tty/serial/8250/8250_port.c       | 25 +++++++++++++++++++----
> >>>    5 files changed, 26 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
> >>> index 52bb21205bb6..770eb00db497 100644
> >>> --- a/drivers/tty/serial/8250/8250.h
> >>> +++ b/drivers/tty/serial/8250/8250.h
> >>> @@ -82,6 +82,7 @@ struct serial8250_config {
> >>>    #define UART_CAP_MINI	(1 << 17)	/* Mini UART on BCM283X family lacks:
> >>>    					 * STOP PARITY EPAR SPAR WLEN5 WLEN6
> >>>    					 */
> >>> +#define UART_CAP_TEMT	(1 << 18)	/* UART has TEMT interrupt */
> >>>    
> >>>    #define UART_BUG_QUOT	(1 << 0)	/* UART has buggy quot LSB */
> >>>    #define UART_BUG_TXEN	(1 << 1)	/* UART has buggy TX IIR status */
> >>> diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
> >>> index 12d03e678295..3881242424ca 100644
> >>> --- a/drivers/tty/serial/8250/8250_bcm2835aux.c
> >>> +++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
> >>> @@ -91,7 +91,7 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev)
> >>>    		return -ENOMEM;
> >>>    
> >>>    	/* initialize data */
> >>> -	up.capabilities = UART_CAP_FIFO | UART_CAP_MINI;
> >>> +	up.capabilities = UART_CAP_FIFO | UART_CAP_MINI | UART_CAP_TEMT;
> >>>    	up.port.dev = &pdev->dev;
> >>>    	up.port.regshift = 2;
> >>>    	up.port.type = PORT_16550;
> >>> diff --git a/drivers/tty/serial/8250/8250_of.c b/drivers/tty/serial/8250/8250_of.c
> >>> index 65e9045dafe6..841f6fcb2878 100644
> >>> --- a/drivers/tty/serial/8250/8250_of.c
> >>> +++ b/drivers/tty/serial/8250/8250_of.c
> >>> @@ -225,6 +225,8 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
> >>>    			&port8250.overrun_backoff_time_ms) != 0)
> >>>    		port8250.overrun_backoff_time_ms = 0;
> >>>    
> >>> +	port8250.capabilities |= UART_CAP_TEMT;
> >>> +
> >>
> >> Shouldn't this be NOT UART_CAP_TEMT set by default? On all other
> >> vendor specific files you enable it, I think here you shouldn't enable
> >> it too by default. Right?
> > 
> > 8250_of does use the em485 emulation - see of_platform_serial_setup()
> > So I did go by the lazy assumption that any 8250 driver using rs485
> > before my series always used the interrupt driver code path, so
> > implicitly required to have the TEMT interrupt.
> > 
> > Of course, you're right that with the 8250_of maybe not all variants
> > actually do have this interrupt, so falling back to the polling here might
> > be safer.
> 
> Probably here it's worth introducing a dt boolean property like
> "temt-capability", then you set or not UART_CAP_TEMT according to its 
> presence in dts. This way all cases are covered and we can act 
> completely through dts files.
> 
> What about that?

Sorry that this was sitting around for over a month.

I think there are two problems with this:

(1) this would break backwards compatibility ... right now the whole code
just assumes that everyone does support the TEMT interrupt, so adding
a property to keep it working would break old DTs, which is something that
should not happen ... I guess one option would be to use the inverse
no-temt-interrupt

(2) uarts handled by 8250_of are still identified by their compatible
though and there is no generic 8250-of compatible, so the
presence / absence of the temt capability should actually just be
bound to the relevant compatible.


So my "gut feeling" is to just keep the current way
(was expecting temt-capability before anyway) until an uart
variant without temt comes along


Heiko



  reply	other threads:[~2020-05-17 15:04 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-25 23:14 [PATCH RFC v2 0/7] serial: 8250: Add rs485 emulation to 8250_dw Heiko Stuebner
2020-03-25 23:14 ` [PATCH DON'T APPLY v2 1/7] serial: Allow uart_get_rs485_mode() to return errno Heiko Stuebner
2020-03-25 23:14 ` [PATCH DON'T APPLY v2 2/7] dt-bindings: serial: Add binding for rs485 bus termination GPIO Heiko Stuebner
2020-03-25 23:14 ` [PATCH DON'T APPLY v2 3/7] serial: 8250: Support " Heiko Stuebner
2020-03-30 14:51   ` Andy Shevchenko
2020-03-25 23:14 ` [PATCH v2 4/7] serial: 8250: Handle implementations not having TEMT interrupt using em485 Heiko Stuebner
2020-03-25 23:47   ` Giulio Benetti
2020-03-26  0:05     ` Heiko Stübner
2020-03-26  2:02       ` Giulio Benetti
2020-05-17 15:04         ` Heiko Stübner [this message]
2020-05-17 17:28           ` Giulio Benetti
2020-03-30 14:52   ` Andy Shevchenko
2020-05-02 13:49   ` Lukas Wunner
2020-05-05 16:38     ` Maarten Brock
2020-05-17 22:01     ` Heiko Stübner
2020-03-25 23:14 ` [PATCH v2 5/7] dt-bindings: serial: Add binding for rs485 receiver enable GPIO Heiko Stuebner
2020-03-30 14:54   ` Andy Shevchenko
2020-05-02 13:51   ` Lukas Wunner
2020-03-25 23:14 ` [PATCH v2 6/7] serial: 8250: Support separate rs485 rx-enable GPIO Heiko Stuebner
2020-03-30 14:56   ` Andy Shevchenko
2020-05-16 20:14   ` Lukas Wunner
2020-03-25 23:14 ` [PATCH v2 7/7] serial: 8250_dw: add em485 support Heiko Stuebner
2020-05-06 15:25   ` Andy Shevchenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=3036126.9QgpAzkLCg@diego \
    --to=heiko@sntech.de \
    --cc=andriy.shevchenko@linux.intel.com \
    --cc=christoph.muellner@theobroma-systems.com \
    --cc=giulio.benetti@micronovasrl.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=jslaby@suse.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=lukas@wunner.de \
    --cc=matwey.kornilov@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).