From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Sultan Alsawaf <sultan@kerneltoast.com>,
Andi Shyti <andi.shyti@intel.com>
Cc: jarkko.nikula@linux.intel.com, aaron.ma@canonical.com,
admin@kryma.net, benjamin.tissoires@redhat.com,
hdegoede@redhat.com, hn.chen@weidahitech.com, jikos@kernel.org,
kai.heng.feng@canonical.com, linux-i2c@vger.kernel.org,
linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
mika.westerberg@linux.intel.com, vicamo.yang@canonical.com,
wsa@kernel.org
Subject: Re: [PATCH v2] HID: i2c-hid: Use block reads when possible to save power
Date: Tue, 16 Jun 2020 19:41:01 +0300 [thread overview]
Message-ID: <20200616164101.GY2428291@smile.fi.intel.com> (raw)
In-Reply-To: <20200616154951.3050-1-sultan@kerneltoast.com>
On Tue, Jun 16, 2020 at 08:49:51AM -0700, Sultan Alsawaf wrote:
> From: Sultan Alsawaf <sultan@kerneltoast.com>
>
> We have no way of knowing how large an incoming payload is going to be,
> so the only strategy available up until now has been to always retrieve
> the maximum possible report length over i2c, which can be quite
> inefficient. For devices that send reports in block read format, the i2c
> controller driver can read the payload length on the fly and terminate
> the i2c transaction early, resulting in considerable power savings.
>
> On a Dell Precision 15 5540 with an i9-9880H, resting my finger on the
> touchpad causes psys power readings to go up by about 4W and hover there
> until I remove my finger. With this patch, my psys readings go from 4.7W
> down to 3.1W, yielding about 1.6W in savings. This is because my
> touchpad's max report length is 60 bytes, but all of the regular reports
> it sends for touch events are only 32 bytes, so the i2c transfer is
> roughly halved for the common case.
> + /* Try to do a block read if the size fits in one byte */
> + flags = size > 255 ? I2C_M_RD : I2C_M_RD | I2C_M_RECV_LEN;
AFAIR SMBus specification tells about 256. Why 255?
Andi, am I correct?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2020-06-16 16:41 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-14 21:02 [PATCH 0/2] i2c-hid: Save power by reducing i2c xfers with block reads Sultan Alsawaf
2020-06-14 21:02 ` [PATCH 1/2] i2c: designware: Only check the first byte for SMBus block read length Sultan Alsawaf
2020-06-15 9:40 ` Andy Shevchenko
2020-06-15 16:03 ` Sultan Alsawaf
2020-06-15 16:07 ` Andy Shevchenko
2020-06-15 17:15 ` Sultan Alsawaf
2020-06-16 13:22 ` Jarkko Nikula
2020-06-16 15:43 ` [PATCH v2] " Sultan Alsawaf
2020-06-17 11:08 ` Jarkko Nikula
2020-06-14 21:02 ` [PATCH 2/2] HID: i2c-hid: Use block reads when possible to save power Sultan Alsawaf
2020-06-16 13:43 ` Jarkko Nikula
2020-06-16 15:49 ` [PATCH v2] " Sultan Alsawaf
2020-06-16 16:41 ` Andy Shevchenko [this message]
2020-06-16 17:18 ` Andi Shyti
2020-06-16 17:32 ` Sultan Alsawaf
2020-06-16 18:02 ` Andi Shyti
2020-06-16 18:17 ` Sultan Alsawaf
2020-06-17 11:17 ` Jarkko Nikula
2020-06-29 17:43 ` Sultan Alsawaf
2020-07-01 8:04 ` Jarkko Nikula
2020-07-01 15:00 ` Sultan Alsawaf
2020-07-03 11:18 ` Jarkko Nikula
2020-09-14 0:15 ` [PATCH v3] i2c: Squash of SMBus block read patchset " Sultan Alsawaf
[not found] ` <bcf9cd02-13d1-8f87-8ef9-2f05f0b54808@linux.intel.com>
2020-09-15 17:48 ` Sultan Alsawaf
2020-09-16 14:09 ` Jarkko Nikula
2020-09-15 20:44 ` Jiri Kosina
2020-06-22 0:58 ` [HID] 0b987151f0: kmsg.i2c_designware_i2c_designware.#: controller_timed_out kernel test robot
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