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

[Guenter Roeck]

On 07/29/2015 09:20 AM, Aaron Sierra wrote:
> > From: "Lee Jones" <lee.jones@xxxxxxxxxx>
> > Sent: Wednesday, July 29, 2015 10:32:26 AM
> >
> > On Wed, 29 Jul 2015, Aaron Sierra wrote:
> >
> > > > From: "Lee Jones" <lee.jones@xxxxxxxxxx>
> > > > 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().

Guenter

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