linux-kernel - Re: [PATCH 2/4] i2c: at91: implement i2c bus recovery

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Message-ID: <1e70ae35-052b-67cc-27c4-1077c211efd0@microchip.com>
Date:   Thu, 24 Oct 2019 14:08:21 +0000
From:   <Codrin.Ciubotariu@...rochip.com>
To:     <kamel.bouhara@...tlin.com>, <wsa@...-dreams.de>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <Nicolas.Ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
        <Ludovic.Desroches@...rochip.com>, <devicetree@...r.kernel.org>,
        <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/4] i2c: at91: implement i2c bus recovery

On 22.10.2019 10:59, Kamel Bouhara wrote:
> On 21/10/2019 22:20, Wolfram Sang wrote:
>> On Wed, Oct 02, 2019 at 04:46:56PM +0200, Kamel Bouhara wrote:
>>> Implement i2c bus recovery when slaves devices might hold SDA low.
>>> In this case re-assign SCL/SDA to gpios and issue 9 dummy clock pulses
>>> until the slave release SDA.
>>>
>>> Signed-off-by: Kamel Bouhara <kamel.bouhara@...tlin.com>
>>
>> Setting up the bus_recovery looks OK. However, I don't see any call to
>> i2c_recover_bus(), so the bus_recovery is never used. Did you test this
>> and see an effect?
>>
> Indeed, I guess I mess it up while doing some git stuff, it should be 
> called from at91_do_twi_transfer() when the transfer times out...
> I actually tested it and verified the recovery is triggered by pulling 
> the SCL to the ground ...
> 
>> Also, I think we should merge this patch "[PATCH v3] i2c: at91: Send bus
>> clear command if SCL or SDA is down" into this series. The crucial thing
>> for both is when to apply the recovery (at the beginning of a
>> transfer!). The rest is "just" that some HW needs a bus_recovery_info
>> for pinctrl/GPIO handling (from this patch), while other HW needs a
>> bus_recovery_info with a custom recover_bus callback.
>>
>> Opinions?
>>
> I'm OK to merge the two series.

So at the beginning of a new transfer, we should check if SDA (or SCL?) 
is low and, if it's true, only then we should try recover the bus.

Kamel, let me know if I can help with anything.

Best regards,
Codrin