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

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Message-Id: <20201102035433.6774-6-rayagonda.kokatanur@broadcom.com>
Date:   Mon,  2 Nov 2020 22:19:00 -0800
From:   Dhananjay Phadke <dphadke@...ux.microsoft.com>
To:     rayagonda.kokatanur@...adcom.com
Cc:     andriy.shevchenko@...ux.intel.com,
        bcm-kernel-feedback-list@...adcom.com, brendanhiggins@...gle.com,
        dphadke@...ux.microsoft.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: [PATCH v3 5/6] i2c: iproc: handle master read request

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.

Regards,
Dhananjay