linux-kernel - Re: [PATCHv2 0/4] ACPI / LPSS: Solution for two issues seen on Asus T100

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Date:	Fri, 16 May 2014 17:45:12 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	"Li, Aubrey" <aubrey.li@...ux.intel.com>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mike Turquette <mturquette@...aro.org>,
	Jin Yao <yao.jin@...ux.intel.com>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 0/4] ACPI / LPSS: Solution for two issues seen on Asus
 T100

On Fri, 2014-05-16 at 21:37 +0800, Li, Aubrey wrote:
> On 2014/5/16 15:04, Andy Shevchenko wrote:
> > On Fri, 2014-05-16 at 07:29 +0800, Li, Aubrey wrote:
> >> On 2014/5/16 0:11, Mika Westerberg wrote:
> >>> On Thu, May 15, 2014 at 11:59:46PM +0800, Li, Aubrey wrote:
> >>>> On 2014/5/15 22:53, Andy Shevchenko wrote:
> >>>>> On Thu, 2014-05-15 at 22:35 +0800, Li, Aubrey wrote:
> >>>>>> On 2014/5/15 21:40, Heikki Krogerus wrote:
> >>>>>>> Changes since v1:
> >>>>>>> - now using do_div() in clk_fd_recalc_rate() as suggested by Andy
> >>>>>>> - NULL checks for clk_name allocation in acpi_lpss.c
> >>>>>>>
> >>>>>>> This combines two patch sets for LPSS that I had already send for
> >>>>>>> review separately. They conflicted with each other.
> >>>>>>>
> >>>>>>> The first two patches will fix a problem were the context of the
> >>>>>>> private LPSS registers is lost when entering D3. The last two will add
> >>>>>>> support for the M/N dividers on LPSS by adding a new basic clock type
> >>>>>>> for fractional dividers. The UART driver needs support for it in order
> >>>>>>> to get clock rates that suit the requested baud rates.
> >>>>>>
> >>>>>> The major issue in my mind is, this proposal makes a couple between I2C
> >>>>>> designware, HSUART, or probably DMA driver as well with LPSS driver.
> >>>>>
> >>>>> acpi_lpss driver creates platform devices for each found and enumerated
> >>>>> device.
> >>>>
> >>>>> If there no acpi_lpss enabled the drivers work as supposed without it.
> >>>>
> >>>> This is not true.
> >>>
> >>> The drivers work fine on non-LPSS platform. If you make them depend on
> >>> acpi_lpss, you break that.
> >>>
> >>
> >> People don't know the relationship between LPSS driver and I2C/HSUART,
> >> there is nowhere to describe that. If LPSS driver is unchecked, they
> >> will encounter a weird issue which is very hard to figure out what's
> >> going on.
> > 
> > Besides this discussion is off the topic, I could say that LPSS drivers
> > are kinda optional (we won't enforce user to use them) even on some
> > systems where they are present. Relationship is provided by the proper
> > kernel configuration.
> > 
> It is optional previously but definitely not optional after this patch.

I'm sorry, I didn't clearly see what part in this patchset prevents
this.

> The user who uses I2C designeware driver without LPSS now, I2C won't
> work properly on Asus T100.

In that case you specifically enable this driver in the kernel
configuration. T100 may require that driver to be fully functional.

> 
> The proper configuration leads to a question, why a completed I2C
> controller driver doesn't work properly without another LPSS driver. I
> worry about this is hard to maintain in future.
> 
> Do we have a platform configuration to specify LPSS is needed?
> 
> BTW, do we have a system with I2C and HSUART but without LPSS?

I believe we have.


-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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