Messages in this thread |  | | Subject | Re: [PATCH v2 0/4] i2c-hid: Save power by reducing i2c xfers with block reads | From | Jarkko Nikula <> | Date | Wed, 23 Sep 2020 16:59:24 +0300 |
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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>
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