Hi, On 9/22/20 11:19 AM, Jiri Kosina wrote: > On Wed, 16 Sep 2020, Sultan Alsawaf wrote: > >> From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> >> >> 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. Sorry for being slow to respond to this. I have not gotten around to testing this, but I saw another email that this breaks things on at least AMD platforms, so I guess that this is on hold for now ? Regards, Hans
