linux-kernel - Re: [PATCH 1/8] serial: core: only get RS485 termination gpio if supported

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Message-ID: <2dda5707-6f13-6d33-863d-a88b89e88a88@gmx.de>
Date:   Thu, 23 Jun 2022 03:59:25 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        ilpo.jarvinen@...ux.intel.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, vz@...ia.com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        lukas@...ner.de, p.rosenberger@...bus.com,
        Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH 1/8] serial: core: only get RS485 termination gpio if
 supported


Hi,

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@...bus.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/ACPI, then
> they probably want to (opportunistically) have it>
>
> With your change it's possible to have a DTS where GPIO line defined in a
> broken way and user won't ever know about it, if they are using platforms
> without termination support.
>

This behavior is not introduced with this patch, also in the current code the driver
wont inform the user if it does not make use erroneous defined termination GPIO.

This patch at least prevents the driver from allocating and holding a GPIO descriptor across
the drivers lifetime that will never be used.

Furthermore it simplifies the code in patch 2 when we want to set the GPIO, since we can
skip the check whether or not the termination GPIO is supported by the driver.



Regards,
Lino