linux-kernel - Re: [PATCH V5 6/7] i2c: tegra: fix PIO rx/tx residual transfer check

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Message-ID: <78140337-dca0-e340-a501-9e37eca6cc87@nvidia.com>
Date:   Thu, 13 Jun 2019 04:30:20 -0700
From:   Bitan Biswas <bbiswas@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        <linux-i2c@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Peter Rosin <peda@...ntia.se>,
        Wolfram Sang <wsa@...-dreams.de>
CC:     Shardar Mohammed <smohammed@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Mantravadi Karthik <mkarthik@...dia.com>
Subject: Re: [PATCH V5 6/7] i2c: tegra: fix PIO rx/tx residual transfer check



On 6/12/19 7:30 AM, Dmitry Osipenko wrote:
> 11.06.2019 13:51, Bitan Biswas пишет:
>> Fix expression for residual bytes(less than word) transfer
>> in I2C PIO mode RX/TX.
>>
>> Signed-off-by: Bitan Biswas <bbiswas@...dia.com>
>> ---
> 
> [snip]
> 
>>   		/*
>> -		 * Update state before writing to FIFO.  If this casues us
>> +		 * Update state before writing to FIFO.  If this causes us
>>   		 * to finish writing all bytes (AKA buf_remaining goes to 0) we
>>   		 * have a potential for an interrupt (PACKET_XFER_COMPLETE is
>> -		 * not maskable).  We need to make sure that the isr sees
>> -		 * buf_remaining as 0 and doesn't call us back re-entrantly.
>> +		 * not maskable).
>>   		 */
>>   		buf_remaining -= words_to_transfer * BYTES_PER_FIFO_WORD;
> 
> Looks like the comment could be removed altogether because it doesn't
> make sense since interrupt handler is under xfer_lock which is kept
> locked during of tegra_i2c_xfer_msg().
I would push a separate patch to remove this comment because of 
xfer_lock in ISR now.

> 
> Moreover the comment says that "PACKET_XFER_COMPLETE is not maskable",
> but then what I2C_INT_PACKET_XFER_COMPLETE masking does?
> 
I2C_INT_PACKET_XFER_COMPLETE masking support available in Tegra chips 
newer than Tegra30 allows one to not see interrupt after Packet transfer 
complete. With the xfer_lock in ISR the scenario discussed in comment 
can be ignored.

-regards,
  Bitan