linux-kernel - Re: [PATCH] axxia-i2c: use auto cmd for last message

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Date:   Wed, 3 Apr 2019 22:54:02 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
Subject: Re: [PATCH] axxia-i2c: use auto cmd for last message

Hi,

On Thu, Mar 28, 2019 at 11:19:45AM +0000, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> Some recent commits to this driver were trying to make sure the TSS
> interrupt is not generated on busy system due to 25ms timer expiring
> between commands. It can still happen, however if STOP command is not
> issued on time at the end of the transmission. If wait_for_completion in
> axxia_i2c_xfer_msg() would not return after 25ms of getting an
> interrupt, TSS will be generated and idev->err_msg will be set to
> -ETIMEDOUT which will be returned from the axxia_i2c_xfer_msg(), even
> though the transfer did actually succeed (STOP is automatically issued
> when TSS triggers).
> 
> Fortunately, apart from already used manual and sequence commands, the
> controller also has so called auto command. It works just like manual
> mode but it but an automatic STOP is issued when either transfer length
> is met or NAK is received from slave device.
> 
> This patch changes the axxia_i2c_xfer_msg() function so that auto
> command is used for last message in transaction letting hardware manage
> issuing STOP. TSS is disabled just after command transferring last
> message finishes. Auto command, just like sequence, ends with SS
> interrupt instead of SNS so handling of both had to be unified.
> 
> The axxia_i2c_stop() is no longer needed as the transfer can only end
> with following conditions:
> - fully successful - then last message was send by AUTO command and STOP
>   was issued automatically
> - NAK received - STOP is issued automatically by controller
> - arbitration lost - STOP should not be issued as we don't control the
>   bus
> - IP interrupt received - this is sent when transfer length is set to 0
>   for auto/sequence command. The check for that is done before START is
>   send so no STOP is required
> - TSS received between commands - STOP is issued by the controller

I am not sure. Is this a bugfix (= for-current) or more a new feature (=
for-next)?

> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@...ia.com>
> Reviewed-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>

I trust you that Alexander gave the review, but it would be a tad more
'open development' if he could give it as a reply to your patch on the
mailing list.

Thanks,

   Wolfram


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