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Date: Tue, 22 Sep 2020 11:19:00 +0200 (CEST) From: Jiri Kosina <jikos@...nel.org> To: Sultan Alsawaf <sultan@...neltoast.com> cc: linux-i2c@...r.kernel.org, aaron.ma@...onical.com, admin@...ma.net, andriy.shevchenko@...ux.intel.com, benjamin.tissoires@...hat.com, hdegoede@...hat.com, hn.chen@...dahitech.com, jarkko.nikula@...ux.intel.com, kai.heng.feng@...onical.com, linux-input@...r.kernel.org, linux-kernel@...r.kernel.org, mika.westerberg@...ux.intel.com, vicamo.yang@...onical.com, wsa@...nel.org Subject: Re: [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads On Wed, 16 Sep 2020, Sultan Alsawaf wrote: > From: Sultan Alsawaf <sultan@...neltoast.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." > > 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(-) Hans, Benjamin, could you please give this patchset some smoke-testing? It looks good to me, but I'd like it to get some testing from your testing machinery before merging. Thanks, -- Jiri Kosina SUSE Labs
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