linux-kernel - Re: [PATCH v2 5/7] HID: ft260: improve i2c large reads performance

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Date:   Tue, 04 Oct 2022 20:15:56 +0200
From:   Enrik Berkhan <Enrik.Berkhan@...a.de>
To:     Michael Zaidman <michael.zaidman@...il.com>, jikos@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        Guillaume Champagne <champagne.guillaume.c@...il.com>
Subject: Re: [PATCH v2 5/7] HID: ft260: improve i2c large reads performance

Hi Michael,

On Wed, 2022-09-28 at 17:48 +0300, Michael Zaidman wrote:
> After:
> 
> $ sudo ./i2cperf -d 2 -o 2 -s 128 -r 0-0xff 13 0x51 -S
> 
>   Read block via i2ctransfer by chunks
>   -------------------------------------------------------------------
>   data rate(bps)  efficiency(%)  data size(B)  total IOs   IO size(B)
>   -------------------------------------------------------------------
>   49316           85             256           2           128
> 
> Kernel log:
> 
> [  +1.447360] ft260_i2c_write_read: off 0x0 rlen 128 wlen 2
> [  +0.000002] ft260_i2c_write: rep 0xd0 addr 0x51 off 0 len 2 wlen 2 flag 0x2 d[0] 0x0
> [  +0.001633] ft260_xfer_status: bus_status 0x41, clock 100
> [  +0.000190] ft260_xfer_status: bus_status 0x40, clock 100
> [  +0.000001] ft260_i2c_read: rep 0xc2 addr 0x51 len 128 rlen 128 flag 0x7
> [  +0.008617] ft260_raw_event: i2c resp: rep 0xde len 60
> [  +0.008033] ft260_raw_event: i2c resp: rep 0xde len 60
> [  +0.000954] ft260_raw_event: i2c resp: rep 0xd1 len 8

As the ft260 can pack up to 60 bytes into one report, would it make
sense to use a multiple-of-60 size (120 or 180)? Might reduce overhead
by another tiny bit ...

Cheers,
Enrik