linux-kernel - Re: [PATCH v1 6/6] i2c: iproc: handle rx fifo full interrupt

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Date:   Mon, 26 Oct 2020 17:36:04 -0700
From:   Ray Jui <ray.jui@...adcom.com>
To:     Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>,
        Dhananjay Phadke <dphadke@...ux.microsoft.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lori Hikichi <lori.hikichi@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Wolfram Sang <wsa@...nel.org>
Subject: Re: [PATCH v1 6/6] i2c: iproc: handle rx fifo full interrupt



On 10/26/2020 8:13 AM, Rayagonda Kokatanur wrote:
> Hi Dhanajay,
> 
> On Fri, Oct 23, 2020 at 11:12 PM Ray Jui <ray.jui@...adcom.com> wrote:
>>
>>
>>
>> On 10/12/2020 3:03 PM, Dhananjay Phadke wrote:
>>> From: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
>>>
>>> On Sun, 11 Oct 2020 23:52:54 +0530, Rayagonda Kokatanur wrote:
>>>> Add code to handle IS_S_RX_FIFO_FULL_SHIFT interrupt to support
>>>> master write request with >= 64 bytes.
>>>>
>>>> Iproc has a slave rx fifo size of 64 bytes.
>>>> Rx fifo full interrupt (IS_S_RX_FIFO_FULL_SHIFT) will be generated
>>>> when RX fifo becomes full. This can happen if master issues write
>>>> request of more than 64 bytes.
>>>>
>>>
>>> ARM cores run much faster than I2C bus, why would rx fifo go full when
>>> rx interrupt is enabled and bytes are read out by bus driver isr?
>>> Isn't fifo read pointer updated on these byte reads?
>>
>> Hi Rayagonda,
>>
>> Could you please reply on this question? For transactions > 64 bytes, do
>> we batch until RX FIFO is full before we read out the data?
> 
> Sorry I missed this question.
> Yes with current design we are batching 64 bytes for translation > 64 bytes.
> 

So we do batch the transfer and read them in one shot, and that's how
the FIFO full interrupt is being utilized for. That sounds okay to me.

Thanks,

Ray

> Best regards,
> Rayagonda
> 
> 
>>
>> Thanks,
>>
>> Ray
>>
>>> Does controller stretch clock when rx fifo is full (e.g. kernel has
>>> crashed, bus driver isn't draining fifo)?
>>>

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