Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <c4186284-0e77-46b2-716b-1975255b8b34@gmx.de>
Date:   Thu, 30 Jun 2022 01:50:15 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Subject: Re: [PATCH 5/8] dt_bindings: rs485: Correct delay values
Content-Language: en-US
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     gregkh@linuxfoundation.org, jirislaby@kernel.org,
        ilpo.jarvinen@linux.intel.com, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, vz@mleia.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
        lukas@wunner.de, p.rosenberger@kunbus.com,
        Lino Sanfilippo <l.sanfilippo@kunbus.com>
References: <20220622154659.8710-1-LinoSanfilippo@gmx.de>
 <20220622154659.8710-6-LinoSanfilippo@gmx.de>
 <YrSU4eL9hgISg3Y1@smile.fi.intel.com>
 <6c50fdca-aac4-aaf5-ad34-18a60fcc0aa0@gmx.de>
 <YrrR4hItCx56bpxI@smile.fi.intel.com>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
In-Reply-To: <YrrR4hItCx56bpxI@smile.fi.intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk


On 28.06.22 12:03, Andy Shevchenko wrote:
> On Thu, Jun 23, 2022 at 10:17:06PM +0200, Lino Sanfilippo wrote:
>> On 23.06.22 at 18:29, Andy Shevchenko wrote:
>>> On Wed, Jun 22, 2022 at 05:46:56PM +0200, Lino Sanfilippo wrote:
>>>>
>>>> The maximum allowed delay for RTS before and RTS after send is 100 ms=
.
>>>> Adjust the documentation accordingly.
>>>
>>> Is it only documentation issue? If the code allows this to be set high=
er
>>> than 100, we may not change the documentation since this an ABI (from
>>> firmware <--> kernel perspective) we need to support old variants.
>>
>> Well currently the documentation claims that a maximum of 1000 msecs is=
 allowed but
>> nothing actually checks the values read from device tree/ACPI and so it=
 is possible
>> to set much higher values (note that the UART drivers dont check the de=
lays read from
>> DT/ACPI either, the only exception I found is max310x which clamps it t=
o 15 ms).
>>
>> We already have a maximum of 100 ms defined for RTS delays set via TIOC=
SRS485. To be
>> consistent with TIOCSRS485 the same limit is used for DT/ACPI values in=
 this patch.
>>
>> I am aware that this changes the firmware/kernel ABI. But we had a simi=
lar situation when
>> the sanity checks for TIOCSRS485 were introduced
>> (see https://lore.kernel.org/all/20220410104642.32195-2-LinoSanfilippo@=
gmx.de/)
>> since before we did not have those limits for all drivers (some drivers=
 clamped the
>> values itself but many did not care).
>> Furthermore 100 ms is already a very high value for RTS delays (which a=
re usually rather
>> in usecs range). So IMHO the risk is very low to break anything when va=
lues are clamped
>> that are higher than that.
>
> You need to elaborate all this in the commit message to justify the chan=
ge.
>

OK, I see. I will rewrite the commit message then to hopefully make the ra=
tionale behind
the time reduction more clear.

Thanks,
Lino