Messages in this thread | | | Date | Wed, 9 Jul 2008 16:31:01 +0400 | From | Dmitry <> | Subject | Re: [patch 4/4] MFD: Change mfd platform device usage to wrapper platform_device |
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2008/7/9 Ben Dooks <ben-linux@fluff.org>: > On Wed, Jul 09, 2008 at 03:56:54PM +0400, Dmitry wrote: >> 2008/7/9 Ben Dooks <ben-linux@fluff.org>: >> > On Wed, Jul 09, 2008 at 03:31:04PM +0400, Dmitry wrote: >> >> 2008/7/9 Ben Dooks <ben-linux@fluff.org>: >> >> > On Wed, Jul 09, 2008 at 03:15:47PM +0400, Dmitry wrote: >> >> >> 2008/7/9 Ben Dooks <ben-linux@fluff.org>: >> >> >> > This patch changes the mfd core behaviour to wrapper the platform_device >> >> >> > it creates in an struct mfd_device which contains the information >> >> >> > about the cell that was created. >> >> >> > >> >> >> > 1) The creation of the resource list and then passing it to the >> >> >> > platform_device_add_resources() causes the allocation of a >> >> >> > large array on the stack as well as copying the source data >> >> >> > twice (it is copied from the mfd_cell to the temporary array >> >> >> > and then copied into the newly allocated array) >> >> >> > >> >> >> > 2) We can wrapper the platform_device into an mfd_device and use >> >> >> > that to do the platform_device and resource allocation in one >> >> >> > go to reduce the failiure. >> >> >> > >> >> >> > Note, is there actually any reason to pass the sub devices any >> >> >> > information about the cell they are created from? The mfd core >> >> >> > already makes the appropriate resource adjustments and anything >> >> >> > else like clocks should be exported by the clock drivers? >> >> >> > >> >> >> > Signed-off-by: Ben Dooks <ben-linux@fluff.org> >> >> >> >> >> >> >> >> >> NAK. >> >> >> 0) It was discussed yesterday on the list and the decision was to go >> >> >> in a different way. >> >> >> I've provided a bit cleaner patch with the same idea, but then we >> >> >> decided to go in a bit different way. >> >> >> 1) I prefer patch by Mike Rapoport which is more clear and goes in a >> >> >> more correct way. >> >> > >> >> > How "more correct", whilst the patch by Mike makes the platform data >> >> > be passed from the cell, there is no longer any way to get from the >> >> > platform device to the mfd_cell... >> >> >> >> Basically we have two choises for the subdevice driver: >> >> 1) it doesn't know about cells at all (e.g. generic-bl, IIRC). Then we are safe >> >> to loose that "cell" information >> >> 2) If it does use cell information (to get access to hooks), we pass it >> >> via platform_data pointer in the mfd_cell and we are ok with it. >> > >> > Erm, that is complete non-answer. The driver model and various other >> > parts of the kernel are littered with examples of embedding one >> > structure within another to gain an C++ like object inheritance. >> > >> > I've supplied an reasonable example of doing this to create an mfd_cell >> > device from an platform_device without creating an large amount of code >> > and improving the efficiency and code-lineage in the process. I do not >> > see how this isn't "correct" or in any way breaing the current linux >> > model of doing things. >> >> It isn't breaking it. OK. I'm leaving the decision to the MFD or ARM >> maintainers. >> And BTW, nearly the same patch was sent yesterday by me[1]. Is it an independant >> work, or did you miss my sign-off? >> >> [1]: http://permalink.gmane.org/gmane.linux.ports.arm.kernel/44142 > > Hmm, thanks, completely missed because it has a completely un-related > looking title. > >> > >> >> >> >> > The current driver is being inefficent in the way it creates resources >> >> > on the stack and then calls a routine that does an kalloc/memcpy on >> >> > the resources. >> >> >> >> I don't see any inefficiency ATM. >> >> >> >> >> 2) Please examine the tmio-nand driver (was here on the list and on >> >> >> linux-mtd). It uses the mfd_cell >> >> >> to call hooks from the "host" driver (tc6393xb, more to be added soon). >> >> > >> >> > The one posted in [1] does not call these hooks at-all, can ou please >> >> > explain why these hooks are needed in addition to the ones already >> >> > available in the platform device driver? >> >> > >> >> > [1] http://lists.infradead.org/pipermail/linux-mtd/2008-June/022137.html >> >> >> >> + >> >> +static int tmio_hw_init(struct platform_device *dev, struct tmio_nand *tmio) >> >> +{ >> >> + struct mfd_cell *cell = mfd_get_cell(dev); >> >> + const struct resource *nfcr = NULL; >> >> + unsigned long base; >> >> + int i; >> >> + >> >> + for (i = 0; i < cell->num_resources; i++) >> >> + if (!strcmp((cell->resources+i)->name, TMIO_NAND_CONTROL)) >> >> + nfcr = &cell->resources[i]; >> >> + >> >> + if (nfcr == NULL) >> >> + return -ENOMEM; >> >> + >> >> + if (cell->enable) { >> >> + int rc = cell->enable(dev); >> >> + if (rc) >> >> + return rc; >> >> + } >> >> >> >> That cell->enable() is necessary to set up the host (in the tc6393xb >> >> case to enable buffers) >> >> to enable access to the nand. >> > >> > So, the enable/disable calls might be useful, however is there any >> > reason this could not be handled by the clock framework? The suspend/resume >> > entries where not used, and I belive should not be in here. >> >> They should be here for exactly the same reason. They are used by the drivers >> that will be submitted later. E.g. OHCI driver needs such >> suspend/resume handling. > > No, you don't understand. I'll make a rather explicit point about the > very clever way the device tree works since the devices are registered > with their parent device set. > > In the suspend, all sub devices are suspended via their > platform_driver.suspend method before the parent device's suspend method > is called. When resuming, the parent is resumed before calling the > children's platform_driver.resume methods.
Suspending of sub-devices is handled in two places: 1) suspend the state of subdevice (e.g. ohci stores some info) and then 2) sub-device host suspends/disables the cell (e.g. clocks, power, etc). These steps depend completely on the MFD-device, not only on the sub-device.
These two-stage power management is represented by the suspend/resume hooks in the mfd_cell. However, I think we will be able to drop the suspend/resume when/if generic clocks and voltage regulators frameworks get merged.
>> > As noted before, mfd_get_cell() got dropped by [2] >> > >> > [2] http://lists.arm.linux.org.uk/lurker/message/20080708.153450.bb33046d.en.html >> >> Yes, and as I said before it will need some small modifications. >> >> -- >> With best wishes >> Dmitry >> >> ------------------------------------------------------------------- >> List admin: http://lists.arm.linux.org.uk/mailman/listinfo/linux-arm-kernel >> FAQ: http://www.arm.linux.org.uk/mailinglists/faq.php >> Etiquette: http://www.arm.linux.org.uk/mailinglists/etiquette.php > > -- > Ben > > Q: What's a light-year? > A: One-third less calories than a regular year. > >
-- With best wishes Dmitry
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