linux-kernel - Re: [PATCH v3 09/11] serial: 8250_lpss: move Quark code from PCI driver

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Date:	Wed, 4 May 2016 13:04:31 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Bryan O'Donoghue <pure.logic@...us-software.ie>
Cc:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Peter Hurley <peter@...leysoftware.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Puustinen, Ismo" <ismo.puustinen@...el.com>
Subject: Re: [PATCH v3 09/11] serial: 8250_lpss: move Quark code from PCI
 driver

Hi Bryan,

On Wed, May 04, 2016 at 10:51:17AM +0100, Bryan O'Donoghue wrote:
> On Wed, 2016-05-04 at 12:42 +0300, Andy Shevchenko wrote:
> > On Wed, May 4, 2016 at 12:31 PM, Bryan O'Donoghue
> > <pure.logic@...us-software.ie> wrote:
> > > Andy,
> > > 
> > > If you are going to start removing working PCI devices from the PCI
> > > config table in favour of a shim in SERIAL_8250_LPSS then the very
> > > minimum should be some sort of dependency link between
> > > SERIAL_8250_LPSS
> > > and CONFIG_SERIAL_8250_PCI in kconfig.
> > > 
> > > A user could reasonably read the QRK datasheet - switch on
> > > CONFIG_SERIAL_8250_PCI and then wonder why no console output
> > > happened
> > > on boot. S/he shouldn't have to know that devices were moved from
> > > the
> > > PCI driver to an LPSS shim driver or that the 8250_lpss driver now
> > > needs to be selected instead of the intuitively correct 8250_pci
> > > driver.
> > 
> > That is taken care of since default is set to SERIAL_8250 (you even
> > don't need to have PCI driver enabled!).
> > Doesn't work for you?
> 
> The default may be set to SERIAL_8250 but, without the QRK specific
> entry in 8250_pci.c you won't get console output.
> 
> So if you are going to remove the QRK entry from 8250_pci.c and stuff
> it into 8250_lpss.c then 8250_lpss needs to be selected by
> CONFIG_SERIAL_8250_PCI.
> 
> Otherwise the person doing the config needs to know that stuff was
> moved from one file to another - even though it's a PCI device (not an
> LPSS/ACPI enumerated device) - which seems like an unreasonable level
> of knowledge to assume on the part of the user.

The only way the user get's to de-select CONFIG_SERIAL_8250_PCI or
CONFIG_SERIAL_8250_LPSS is if S/he also selects CONFIG_EXPERT, and if
S/he does that then we can assume S/he has the knowledge.

I'm against binding these separated drivers to CONFIG_SERIAL_8250_PCI
because doing that will very fast mean that we also remove the
possibility to de-select CONFIG_SERIAL_8250_PCI when only, for
example, CONFIG_SERIAL_8250_LPSS was wanted.


Thanks,

-- 
heikki