linux-kernel - Re: [PATCH v3 5/6] i2c: iproc: handle master read request

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Message-ID: <861d734f-c776-f70b-e414-a4b32c0f991e@gmail.com>
Date:   Tue, 3 Nov 2020 19:35:49 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Dhananjay Phadke <dphadke@...ux.microsoft.com>,
        rayagonda.kokatanur@...adcom.com
Cc:     andriy.shevchenko@...ux.intel.com,
        bcm-kernel-feedback-list@...adcom.com, brendanhiggins@...gle.com,
        f.fainelli@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        lori.hikichi@...adcom.com, rjui@...adcom.com,
        sbranden@...adcom.com, wsa@...nel.org
Subject: Re: [PATCH v3 5/6] i2c: iproc: handle master read request



On 11/2/2020 10:19 PM, Dhananjay Phadke wrote:
> On Mon,  2 Nov 2020 09:24:32 +0530, Rayagonda Kokatanur wrote:
> 
>> Handle single or multi byte master read request with or without
>> repeated start.
>>
>> Fixes: c245d94ed106 ("i2c: iproc: Add multi byte read-write support for slave mode")
>> Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@...adcom.com>
>> ---
>>  drivers/i2c/busses/i2c-bcm-iproc.c | 215 +++++++++++++++++++++++------
>>  1 file changed, 170 insertions(+), 45 deletions(-)
>>
>> diff --git a/drivers/i2c/busses/i2c-bcm-iproc.c b/drivers/i2c/busses/i2c-bcm-iproc.c
>> index 7a235f9f5884..22e04055b447 100644
>> --- a/drivers/i2c/busses/i2c-bcm-iproc.c
>> +++ b/drivers/i2c/busses/i2c-bcm-iproc.c
>> @@ -160,6 +160,11 @@
>>  
>>  #define IE_S_ALL_INTERRUPT_SHIFT     21
>>  #define IE_S_ALL_INTERRUPT_MASK      0x3f
>> +/*
>> + * It takes ~18us to reading 10bytes of data, hence to keep tasklet
>> + * running for less time, max slave read per tasklet is set to 10 bytes.
>> + */
>> +#define MAX_SLAVE_RX_PER_INT         10
>>  
> 
> In patch [3/6], you've enabled IS_S_RX_THLD_SHIFT in slave ISR bitmask,
> however it's not actually used in processing rx events.
> 
> Instead of hardcoding this threshold here, it's better to add a
> device-tree knob for rx threshold, program it in controller and handle
> that RX_THLD interrupt. This will give more flexibility to drain the rx
> fifo earlier than -
> (1) waiting for FIFO_FULL interrupt for transactions > 64B.
> (2) waiting for start of read transaction in case of master write-read.

The Device Tree is really intended to describe the hardware FIFO size,
not watermarks, as those tend to be more of a policy/work load decision.
Maybe this is something that can be added as a module parameter, or
configurable via ioctl() at some point.
-- 
Florian