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From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
To: Peter Rosin <peda@axentia.se>
Cc: Ajay Gupta <ajayg@nvidia.com>,
	"wsa@the-dreams.de" <wsa@the-dreams.de>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: [v13,2/2] usb: typec: ucsi: add support for Cypress CCGx
Date: Thu, 25 Oct 2018 12:26:12 +0300	[thread overview]
Message-ID: <20181025092612.GC30828@kuha.fi.intel.com> (raw)

Hi Peter,

> > I still didn't understand why can't this just be taken care of in your
> > I2C host driver? Why can't you just read 4 bytes at a time in your
> > master_xfer hook until you have received as much as the message is
> > asking, and only after that return?
> 
> The I2C host hardware *cannot* read more than 4 bytes in any one xfer
> according to the HW designers. Seriously broken crap, that piece of
> hardware... (If that assertion from the HW designers is indeed true?
> I suspect that it can be made to work, but the docs are closed and I
> don't have HW to experiment with, so it remains a suspicion...)
> 
> And the I2C host driver *cannot* be expected to know exactly how any
> one client device needs to split xfers into many when the 4 byte limit
> is getting in the way, and neither can the I2C core. Because I bet
> there are devices where it's not even possible to split xfers while
> keeping semantics equivalent...
> 
> So, every client driver will need to adjust to this quirk if they are
> to operate with this worthless I2C host (or others with similar
> limitations, if there are any?). Fortunately, most client drivers don't
> read in bulk. Unfortunately, many do...

OK, thanks for the explanation.

I think I'm repeating these questions. You guys already went through
this, so sorry for the noise.


Thanks,

             reply	other threads:[~2018-10-25  9:26 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-25  9:26 Heikki Krogerus [this message]
  -- strict thread matches above, loose matches on Subject: below --
2018-10-26 16:25 [v13,2/2] usb: typec: ucsi: add support for Cypress CCGx Ajay Gupta
2018-10-26  7:27 Heikki Krogerus
2018-10-26  6:49 Peter Rosin
2018-10-25 21:55 Ajay Gupta
2018-10-25 21:30 Ajay Gupta
2018-10-25 21:29 Ajay Gupta
2018-10-25  9:26 Andy Shevchenko
2018-10-25  9:07 Peter Rosin
2018-10-25  8:17 Heikki Krogerus
2018-10-24 17:43 Ajay Gupta
2018-10-24  9:25 Andy Shevchenko
2018-10-23 18:56 Ajay Gupta
2018-10-23  9:35 Heikki Krogerus
2018-10-03 18:27 Ajay Gupta

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