From: Sultan Alsawaf <sultan@kerneltoast.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Aaron Ma <aaron.ma@canonical.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>,
Jiri Kosina <jikos@kernel.org>,
Kai-Heng Feng <kai.heng.feng@canonical.com>,
linux-i2c <linux-i2c@vger.kernel.org>,
linux-input <linux-input@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
Pavel Balan <admin@kryma.net>, Tin Huynh <tnhuynh@apm.com>,
Wolfram Sang <wsa@kernel.org>,
You-Sheng Yang <vicamo.yang@canonical.com>
Subject: Re: [PATCH 1/2] i2c: designware: Only check the first byte for SMBus block read length
Date: Mon, 15 Jun 2020 10:15:08 -0700 [thread overview]
Message-ID: <20200615171508.GA2663@sultan-book.localdomain> (raw)
In-Reply-To: <CAHp75Ve1TgRrKF0_d-7dY6EZU36QszwQ1ezwE03RERKywCxGYg@mail.gmail.com>
On Mon, Jun 15, 2020 at 07:07:42PM +0300, Andy Shevchenko wrote:
> On Mon, Jun 15, 2020 at 7:06 PM Sultan Alsawaf <sultan@kerneltoast.com> wrote:
> > On Mon, Jun 15, 2020 at 12:40:19PM +0300, Andy Shevchenko wrote:
> > > On Sun, Jun 14, 2020 at 02:02:54PM -0700, Sultan Alsawaf wrote:
> > > > From: Sultan Alsawaf <sultan@kerneltoast.com>
> > > >
> > > > SMBus block reads can be broken because the read function will just skip
> > > > over bytes it doesn't like until reaching a byte that conforms to the
> > > > length restrictions for block reads. This is problematic when it isn't
> > > > known if the incoming payload is indeed a conforming block read.
> > > >
> > > > According to the SMBus specification, block reads will only send the
> > > > payload length in the first byte, so we can fix this by only considering
> > > > the first byte in a sequence for block read length purposes.
> > >
> > > I'm wondering if this overlaps with [1]. AFAIU that one is also makes sure that
> > > the length is not a garbage.
> > >
> > > [1]: https://lore.kernel.org/linux-i2c/20200613104109.2989-1-mans@mansr.com/T/#u
> >
> > No overlap.
>
> Thanks for clarifying.
>
> > That looks like a similar bug for a different driver. In my case,
> > the adapter provides native SMBus support, so emulation is never used. This is
> > clear to see by looking at i2c_transfer_buffer_flags(), which only uses the
> > master_xfer functions provided by the adapter; it doesn't call the emulation
> > path at all.
>
> But do we get an advantage if this can be done in the i2c core instead
> (once for all)?
We can't, because the adapter driver needs to know mid-transfer to look for the
payload length in the first byte, and then alter the transfer size on-the-fly.
That can't be done in the i2c core, sadly. The problem is that we don't know if
a transfer is going to be a block read or not beforehand. And altering the
transfer size mid-transfer is definitely a controller specific task.
Sultan
next prev parent reply other threads:[~2020-06-15 17:15 UTC|newest]
Thread overview: 26+ 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 [this message]
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
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
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