From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: 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>,
Jarkko Nikula <jarkko.nikula@linux.intel.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: Thu, 17 Sep 2020 17:02:27 +0300 [thread overview]
Message-ID: <CAHp75Vea8=WchmWVOGndgarjehv+sYQh7CNUrQYqmG8hGJCzHA@mail.gmail.com> (raw)
In-Reply-To: <20200917052256.5770-1-sultan@kerneltoast.com>
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.
>
> Sultan
>
> Sultan Alsawaf (4):
> i2c: designware: Fix transfer failures for invalid SMBus block reads
> i2c: designware: Ensure tx_buf_len is nonzero for SMBus block reads
> i2c: designware: Allow SMBus block reads up to 255 bytes in length
> HID: i2c-hid: Use block reads when possible to save power
>
> drivers/hid/i2c-hid/i2c-hid-core.c | 5 ++++-
> drivers/i2c/busses/i2c-designware-master.c | 15 +++++++++------
> 2 files changed, 13 insertions(+), 7 deletions(-)
>
> --
> 2.28.0
>
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-09-17 14:45 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 ` Andy Shevchenko [this message]
2020-09-23 13:59 ` [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads Jarkko Nikula
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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