netdev - Re: [PATCH net-next V2] net: dsa: microchip: Adjust reset release timing to match reference reset circuit

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Date:   Wed, 20 Jan 2021 18:10:59 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Marek Vasut <marex@...x.de>, Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Paul Barker <pbarker@...sulko.com>
Subject: Re: [PATCH net-next V2] net: dsa: microchip: Adjust reset release
 timing to match reference reset circuit



On 1/20/2021 5:51 PM, Marek Vasut wrote:
> On 1/21/21 2:31 AM, Jakub Kicinski wrote:
>> On Wed, 20 Jan 2021 04:05:02 +0100 Marek Vasut wrote:
>>> KSZ8794CNX datasheet section 8.0 RESET CIRCUIT describes recommended
>>> circuit for interfacing with CPU/FPGA reset consisting of 10k pullup
>>> resistor and 10uF capacitor to ground. This circuit takes ~100 ms to
>>> rise enough to release the reset.
>>>
>>> For maximum supply voltage VDDIO=3.3V VIH=2.0V R=10kR C=10uF that is
>>>                      VDDIO - VIH
>>>    t = R * C * -ln( ------------- ) = 10000*0.00001*-(-0.93)=0.093 s
>>>                         VDDIO
>>> so we need ~95 ms for the reset to really de-assert, and then the
>>> original 100us for the switch itself to come out of reset. Simply
>>> msleep() for 100 ms which fits the constraint with a bit of extra
>>> space.
>>>
>>> Fixes: 5b797980908a ("net: dsa: microchip: Implement recommended
>>> reset timing")
>>> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>>> Signed-off-by: Marek Vasut <marex@...x.de>
>>
>> I'm slightly confused whether this is just future proofing or you
>> actually have a board where this matters. The tree is tagged as
>> net-next but there is a Fixes tag which normally indicates net+stable.
> 
> I have a board where I trigger this problem, that's how I found it. It
> should be passed to stable too. So the correct tree / tag is "net" ?

If this is a bug fix for a commit that is not only in 'net-next', then
yes, targeting 'net' is more appropriate:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/networking/netdev-FAQ.rst#n28
-- 
Florian