linux-kernel - Re: [PATCH 12/12] i2c: xiic: Correct the BNB interrupt enable sequence

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Date:   Wed, 29 Jun 2022 15:13:46 +0200
From:   Krzysztof Adamski <krzysztof.adamski@...ia.com>
To:     Manikanta Guntupalli <manikanta.guntupalli@...inx.com>,
        michal.simek@...inx.com, michal.simek@....com,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org, git@....com
Cc:     Srinivas Goud <srinivas.goud@...inx.com>
Subject: Re: [PATCH 12/12] i2c: xiic: Correct the BNB interrupt enable
 sequence

W dniu 24.06.2022 o 14:05, Manikanta Guntupalli pisze:
> From: Srinivas Goud <srinivas.goud@...inx.com>
>
> With updated AXI IIC IP core(v2.1)there is change in IP behavior
> in dynamic mode, where controller initiate read transfer on IIC
> bus only after getting the value for the number of bytes to receive.
>
> In the existing xiic_start_recv function Bus Not Busy(BNB)
> interrupt is enabled just after "slave address + start"
> write to FIFO and before the "count + stop"write to FIFO.
> Since IIC controller drives the start address of a transaction
> on the bus only after it has received the byte count information
> the above sequence can lead to spurious BNB interrupt in case
> there is any delay after "slave address + start" write to FIFO.
>
> This is fixed by ensuring that BNB interrupt is enabled only
> after "count + stop" has been written to FIFO.
>
> Signed-off-by: Srinivas Goud <srinivas.goud@...inx.com>
> Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@...inx.com>
> ---

[...]

Does this spurious interrupt cause any trouble or it is just ignored and 
the only problem is unneeded extra CPU load?

Krzysztof