linux-kernel - Re: [PATCH 1/5] iTCO_wdt: Expose watchdog properties using platform data

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Message-ID: <1406016742.308627.1438189252821.JavaMail.zimbra@xes-inc.com>
Date:	Wed, 29 Jul 2015 12:00:52 -0500 (CDT)
From:	Aaron Sierra <asierra@...-inc.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Lee Jones <lee.jones@...aro.org>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Wim Van Sebroeck <wim@...ana.be>,
	linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Jean Delvare <jdelvare@...e.com>,
	Wolfram Sang <wsa@...-dreams.de>,
	Matt Fleming <matt.fleming@...el.com>,
	Peter Tyser <ptyser@...-inc.com>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [PATCH 1/5] iTCO_wdt: Expose watchdog properties using platform
 data

----- Original Message -----
> From: "Guenter Roeck" <linux@...ck-us.net>
> Sent: Wednesday, July 29, 2015 11:38:08 AM
> 
> On 07/29/2015 09:20 AM, Aaron Sierra wrote:
> >> From: "Lee Jones" <lee.jones@...aro.org>
> >> Sent: Wednesday, July 29, 2015 10:32:26 AM
> >>
> >> On Wed, 29 Jul 2015, Aaron Sierra wrote:
> >>
> >>>> From: "Lee Jones" <lee.jones@...aro.org>
> >>>> Sent: Wednesday, July 29, 2015 2:38:41 AM
> >>>>
> >>>> On Tue, 28 Jul 2015, Aaron Sierra wrote:
> >>>>
> >>>>>>>>> @@ -933,7 +956,7 @@ gpe0_done:
> >>>>>>>>>   	lpc_chipset_info[priv->chipset].use_gpio = ret;
> >>>>>>>>>   	lpc_ich_enable_gpio_space(dev);
> >>>>>>>>>
> >>>>>>>>> -	lpc_ich_finalize_cell(dev, &lpc_ich_cells[LPC_GPIO]);
> >>>>>>>>> +	lpc_ich_finalize_gpio_cell(dev);
> >>>>>>>>>   	ret = mfd_add_devices(&dev->dev, PLATFORM_DEVID_AUTO,
> >>>>>>>>>   			      &lpc_ich_cells[LPC_GPIO], 1, NULL, 0, NULL);
> >>>>>>>>>
> >>>>>>>>> @@ -1007,7 +1030,10 @@ static int lpc_ich_init_wdt(struct
> >>>>>>>>> pci_dev
> >>>>>>>>> *dev)
> >>>>>>>>>   		res->end = base_addr + ACPIBASE_PMC_END;
> >>>>>>>>>   	}
> >>>>>>>>>
> >>>>>>>>> -	lpc_ich_finalize_cell(dev, &lpc_ich_cells[LPC_WDT]);
> >>>>>>>>> +	ret = lpc_ich_finalize_wdt_cell(dev);
> >>>>>>>>> +	if (ret)
> >>>>>>>>> +		goto wdt_done;
> >>>>>>>>> +
> >>>>>>>>>   	ret = mfd_add_devices(&dev->dev, PLATFORM_DEVID_AUTO,
> >>>>>>>>>   			      &lpc_ich_cells[LPC_WDT], 1, NULL, 0, NULL);
> >>>>>>>>
> >>>>>>>> Why do you have an mfd_add_devices() call for each device?
> >>>>>>>
> >>>>>>> Good question. This call has been present since March 2012 when
> >>>>>>> support
> >>>>>>> was first added for iTCO_wdt in commit 887c8ec7219f ("watchdog:
> >>>>>>> Convert
> >>>>>>> iTCO_wdt driver to mfd model").
> >>>>>>>
> >>>>>>> There's no good reason that I can see. Aaron?
> >>>>>
> >>>>> I chose to call mfd_add_devices() in each device init function
> >>>>> because I thought it was the easiest way to avoid registering an
> >>>>> incomplete/invalid MFD cell should an error occur during init.
> >>>>>
> >>>>> That way device registration wouldn't be an all-or-nothing affair.
> >>>>>
> >>>>> Doesn't mfd_add_devices() bail out after the first unsuccessful
> >>>>> mfd to platform device translation?
> >>>>
> >>>> Right, as it should.
> >>>>
> >>>> Under what circumstance would an error occur and you'd wish to carry
> >>>> on registering devices?
> >>>
> >>> Lee,
> >>>
> >>> The two devices that this driver is responsible for are conceptually
> >>> independent; they simply are lumped together in one PCI device. No
> >>> failure while preparing resources for the watchdog device should
> >>> prevent the GPIO device from being registered.
> >>
> >> This makes me think that perhaps this isn't an MFD at all then?
> >>
> >> Perhaps I should invest some time to looking into that.
> >>
> >>> The most common real world circumstance that I experience is when a
> >>> BIOS reserves resources associated with the GPIO device, thus
> >>> preventing the GPIO resources (ICH_RES_GPE0 and/or ICH_RES_GPIO) from
> >>> being fully prepared.
> >>>
> >>> I have not experienced issues with the watchdog device, but a similar
> >>> issue would exist if the RCBA were disabled in a "v2" device.
> >>>
> >>> It seems like a dangerous change to simply attempt to register both
> >>> of these devices with a single call, when one or both of them could
> >>> be incomplete.
> >>>
> >>> Perhaps your real issue with this driver structure is that these
> >>> cells are elements of a single lpc_ich_cells array for no clear
> >>> reason. If each had a dedicated mfd_cell variable, would that be
> >>> more acceptable to you?
> >>>
> >>> -static struct mfd_cell lpc_ich_cells[] = {
> >>> +static struct mfd_cell lpc_ich_wdt_cell = {
> >>> ...
> >>> +static struct mfd_cell lpc_ich_gpio_cell = {
> >>>
> >>> That would eliminate the need for the lpc_cells enum, too.
> >>
> >> Yes, that would make more sense.  Also consider using mfd_add_device()
> >> instead of mfd_add_devices(), as you are only attempting registration
> >> for a single device.
> >>
> >
> > I can submit a patch the splits up the array elements, but I
> > only see mfd_add_device() as a static function in mfd-core.c;
> > Is that being exported in a development branch somewhere?
> >
>
> Sure you want to do that ? You might have to move usage count
> handling into the calling driver, and also provide mfd_remove_device().

Nope, just the array split-up! Thanks Guenter.

-Aaron S.
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