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Subject: Re: [PATCH 1/8] serial: core: only get RS485 termination gpio if
 supported
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        =?UTF-8?Q?Ilpo_J=c3=a4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Vladimir Zapolskiy <vz@mleia.com>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        devicetree <devicetree@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Lukas Wunner <lukas@wunner.de>, p.rosenberger@kunbus.com,
        Lino Sanfilippo <l.sanfilippo@kunbus.com>
References: <20220622154659.8710-1-LinoSanfilippo@gmx.de>
 <20220622154659.8710-2-LinoSanfilippo@gmx.de>
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 <2dda5707-6f13-6d33-863d-a88b89e88a88@gmx.de>
 <CAHp75Vd_ix=bJs9k6bYM8S+3f_Pw7Tvs9DhPcZxu1=33T=mQ7A@mail.gmail.com>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
Message-ID: <52ea773c-b5b0-fc4d-9b85-022676778af7@gmx.de>
Date:   Thu, 23 Jun 2022 18:08:56 +0200
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On 23.06.22 at 11:45, Andy Shevchenko wrote:
> On Thu, Jun 23, 2022 at 4:00 AM Lino Sanfilippo <LinoSanfilippo@gmx.de> =
wrote:
>> On 22.06.22 at 19:04, Andy Shevchenko wrote:
>>> On Wed, Jun 22, 2022 at 05:46:52PM +0200, Lino Sanfilippo wrote:
>>>> From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
>>>>
>>>> In uart_get_rs485_mode() only try to get a termination GPIO if RS485 =
bus
>>>> termination is supported by the driver.
>>>
>>> I'm not sure I got the usefulness of this change.
>>> We request GPIO line as optional, so if one is defined it in the DT/AC=
PI, then
>>> they probably want to (opportunistically) have it>
>>>
>>> With your change it's possible to have a DTS where GPIO line defined i=
n a
>>> broken way and user won't ever know about it, if they are using platfo=
rms
>>> without termination support.
>>
>> This behavior is not introduced with this patch, also in the current co=
de the driver
>> wont inform the user if it does not make use erroneous defined terminat=
ion GPIO.
>
> It does. If a previously stale GPIO resource may have deferred a probe
> and hence one may debug why the driver is not working, after this
> change one may put a stale GPIO resource into DT/ACPI and have nothing
> in the result. Meaning the change relaxes validation which I consider
> is not good.
>

Ok I see the point. So what about changing it to:

	if (port->rs485_term_gpio &&
	    !(port->rs485_supported->flags & SER_RS485_TERMINATE_BUS)) {
		dev_warn(port->dev,
			"%s (%d): RS485 termination gpio not supported by driver\n",
			port->name, port->line);
		devm_gpiod_put(dev, port->rs485_term_gpio);
		port->rs485_term_gpio =3D NULL;
	}

This would also be consistent to the warnings we print in uart_sanitize_se=
rial_rs485() for invalid
RS485 settings.


Regards,
Lino