From: Jarkko Nikula <jarkko.nikula@linux.intel.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>,
Sultan Alsawaf <sultan@kerneltoast.com>
Cc: linux-i2c <linux-i2c@vger.kernel.org>,
Jiri Kosina <jikos@kernel.org>, Aaron Ma <aaron.ma@canonical.com>,
Pavel Balan <admin@kryma.net>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Benjamin Tissoires <benjamin.tissoires@redhat.com>,
Hans de Goede <hdegoede@redhat.com>,
HungNien Chen <hn.chen@weidahitech.com>,
Kai-Heng Feng <kai.heng.feng@canonical.com>,
linux-input <linux-input@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
You-Sheng Yang <vicamo.yang@canonical.com>,
Wolfram Sang <wsa@kernel.org>
Subject: Re: [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads
Date: Wed, 23 Sep 2020 16:59:24 +0300 [thread overview]
Message-ID: <86cbe3f2-30c9-615e-6d29-c94c98d6be53@linux.intel.com> (raw)
In-Reply-To: <CAHp75Vea8=WchmWVOGndgarjehv+sYQh7CNUrQYqmG8hGJCzHA@mail.gmail.com>
On 9/17/20 5:02 PM, Andy Shevchenko wrote:
> On Thu, Sep 17, 2020 at 8:26 AM Sultan Alsawaf <sultan@kerneltoast.com> wrote:
>>
>> From: Sultan Alsawaf <sultan@kerneltoast.com>
>>
>> This is a fixed resubmission of "[PATCH 0/2] i2c-hid: Save power by reducing i2c
>> xfers with block reads". That original patchset did not have enough fixes for
>> the designware i2c adapter's I2C_M_RECV_LEN feature, which is documented
>> extensively in the original email thread.
>>
>> Here is the original cover letter, which still applies:
>> "I noticed on my Dell Precision 15 5540 with an i9-9880H that simply putting my
>> finger on the touchpad would increase my system's power consumption by 4W, which
>> is quite considerable. Resting my finger on the touchpad would generate roughly
>> 4000 i2c irqs per second, or roughly 20 i2c irqs per touchpad irq.
>>
>> Upon closer inspection, I noticed that the i2c-hid driver would always transfer
>> the maximum report size over i2c (which is 60 bytes for my touchpad), but all of
>> my touchpad's normal touch events are only 32 bytes long according to the length
>> byte contained in the buffer sequence.
>>
>> Therefore, I was able to save about 2W of power by passing the I2C_M_RECV_LEN
>> flag in i2c-hid, which says to look for the payload length in the first byte of
>> the transfer buffer and adjust the i2c transaction accordingly. The only problem
>> though is that my i2c controller's driver allows bytes other than the first one
>> to be used to retrieve the payload length, which is incorrect according to the
>> SMBus spec, and would break my i2c-hid change since not *all* of the reports
>> from my touchpad are conforming SMBus block reads.
>>
>> This patchset fixes the I2C_M_RECV_LEN behavior in the designware i2c driver and
>> modifies i2c-hid to use I2C_M_RECV_LEN to save quite a bit of power. Even if the
>> peripheral controlled by i2c-hid doesn't support block reads, the i2c controller
>> drivers should cope with this and proceed with the i2c transfer using the
>> original requested length."
>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> for I²C DesignWare patches.
>
Also for i2c-designware
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
next prev parent reply other threads:[~2020-09-23 13:59 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-17 5:22 [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads Sultan Alsawaf
2020-09-17 5:22 ` [PATCH v2 1/4] i2c: designware: Fix transfer failures for invalid SMBus " Sultan Alsawaf
2020-09-17 5:22 ` [PATCH v2 2/4] i2c: designware: Ensure tx_buf_len is nonzero for " Sultan Alsawaf
2020-09-17 12:47 ` Andy Shevchenko
2020-09-17 13:44 ` Jarkko Nikula
2020-09-17 14:45 ` Andy Shevchenko
2020-09-17 5:22 ` [PATCH v2 3/4] i2c: designware: Allow SMBus block reads up to 255 bytes in length Sultan Alsawaf
2020-09-17 20:57 ` Wolfram Sang
2020-09-17 23:12 ` Sultan Alsawaf
2020-09-17 5:22 ` [PATCH v2 4/4] HID: i2c-hid: Use block reads when possible to save power Sultan Alsawaf
2020-09-17 14:02 ` [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads Andy Shevchenko
2020-09-23 13:59 ` Jarkko Nikula [this message]
2020-09-22 9:19 ` Jiri Kosina
2020-09-22 11:36 ` Wolfram Sang
2020-09-22 19:59 ` Jiri Kosina
2020-09-23 6:02 ` Sultan Alsawaf
2020-10-16 11:16 ` Hans de Goede
2020-10-16 15:24 ` Sultan Alsawaf
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