On Mon, Oct 27, 2014 at 05:52:02PM +0200, Pantelis Antoniou wrote: > Hi Steffen, > > > On Oct 27, 2014, at 17:23 , Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> wrote: > > > > Hi! > > > > On Mon, Oct 27, 2014 at 01:54:20PM +0200, Pantelis Antoniou wrote: > >> Hi Stefen, > >> > >>> On Oct 25, 2014, at 17:42 , Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> wrote: > >>> > >>> Hi Pantelis! > >>> > >>> On Fri, Oct 24, 2014 at 12:20:53PM +0300, Pantelis Antoniou wrote: > >>>> Hi Stefan, Allan, > >>>> > >>>> Sorry, haven’t had a chance to review all this yet; will do so in the weekend. > >>>> Just wanted to pop in and comment on a few things. > >>>> > >>>>> On Oct 24, 2014, at 10:00 AM, Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx> wrote: > >>>>> > >>>>> Hi! > >>>>> > >>>>> On Thu, Oct 23, 2014 at 06:51:06PM -0500, atull@xxxxxxxxxxxxxxxxxxxxx wrote: > >>>>>> From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx> > >>>>> > >>>>> (...) > >>>>> > >>>>>> diff --git a/Documentation/devicetree/bindings/fpga/altera-hps2fpga-bridge.txt b/Documentation/devicetree/bindings/fpga/altera-hps2fpga-bridge.txt > >>>>>> new file mode 100644 > >>>>>> index 0000000..bc24a2e > >>>>>> --- /dev/null > >>>>>> +++ b/Documentation/devicetree/bindings/fpga/altera-hps2fpga-bridge.txt > >>>>>> @@ -0,0 +1,53 @@ > >>>>>> +Altera FPGA/HPS Bridge Driver > >>>>>> + > >>>>>> +This driver manages a bridge between a FPGA and a host processor system (HPS). > >>>>>> +User space can enable or disable the bridge by writing a "1" or a "0", > >>>>>> +respectively, to its enable file under bridge's entry in > >>>>>> +/sys/class/fpga-bridge. Typically, one disables the bridges before > >>>>>> +reprogramming the FPGA. Once the FPGA is reprogrammed, the bridges are > >>>>>> +reenabled. > >>>>>> + > >>>>> > >>>>> NAK. > >>>>> > >>>>> This is all linux specific and doesn't belong here. > >>>>> > >>>> > >>>> We know. The DT spec hasn’t been updated for a while, and this is going to be > >>>> part of what we want to do with the restarting of the ePAPR spec process. > >>>> > >>> > >>> As we don't have a new spec yet, I go with the current state of the art. > >>> And I don't see how "file under ... /sys/class/fpga-bridge" fits the > >>> current spec. > >>> > >>>> So absolutes like “DT is a hardware description only" might be too strong statements, that > >>>> do not work in practice anymore. > >>>> > >>>> There’s no such thing as pure hardware devices lately - there is always a configuration > >>>> component; some of it OS specific, some of it not. > >>>> > >>> > >>> If it really is necessary, I'm not against it, don't get me wrong. > >>> But in the grand scheme I wouldn't say that this fits my experience. > >>> There are some devices that need configuration and often when it is > >>> done in the DT, it is just a shortcut or not thought through. > >>> And can be also introspected dynamically. With some discussion on the > >>> list these bindings often change. > >>> > >> > >> Already answered and given a possible way this might work; admittedly this > >> specific example is not a good fit for what I was trying to say, but whatever. > >> Let’s get the ball rolling. > >> > > > > I would be okay with chosen-node. Not for this driver; but in general. > > > > Let’s figure out how to do it then… > > >>> Regarding OS specifics: already there, e.g. console setup in the chosen node. > >>> And other things I saw are ethernet aliases just for u-boot. Not a problem > >>> of the spec, just a problem of u-boot and unneccessary "configuration". > >>> Just to fix a bad bootloader. barebox can handle this without any > >>> such stuff. Maybe we should integrate the DT "overlays" barebox uses into > >>> the in-kernel DTs as well...but does it really help/interest someone who > >>> decides to use u-boot where barebox stores its environment? I guess not. > >>> > >> > >> Although I’m not against having DT overlays in the bootloader, I only see them > >> as a method that helps a platform developer express things easier. I am completely > >> against having the kernel tied to any particular bootloader. > >> > >> We’ve all been through the hell where a kernel only boots if the bootloader has > >> setup the platform “correctly”. This “correctly” has a very loose definition and > >> 99/100 times is extremely badly documented or not at all. > >> > >> IMHO the bootloader should (as part of the normal boot sequence) only setup the > >> absolutely bare minimum and then pass control to the kernel as soon as possible. > >> > >> The full featured bootloader environment should only be presented when the user > >> requests so. > >> > > > > Totally agree. The kernel shouldn't be tied to any bootloader if at all possible > > (the SoCFPGA is an especially bad example here again, as the pinmuxing can only > > happen in the bootloader). > > I’m not familiar with SoCFPGA. Why pinmuxing is only possible in the bootloader? > Can’t the bootloader configure the minimum pinmux config and then have Linux setup > the rest? > > If we’re feeling particularly nasty, we might just require bootloaders to clean the > hardware state before passing control to Linux (besides memory controller setup) and > see what’s broken. > Okay, offtopic, but: a) datasheet explicitely states that dynamic pinmuxing is not supported. b) last time I checked, no documentation at all. You get some magic values spit out by Altera's tools. c) you don't have registers. Pinmuxing is done via JTAG scan chain; which you feed the magic values. Apart from that, it seems to be the most sane idea, to at least write your driver in a way, that doesn't make any assumptions on HW state. But I think this is already common practice in mainline. > > But should the DT include stuff than, that is only interesting for linux? > > > > Like it or not it’s Linux that’s in the forefront of many hardware designs. > I like it; pays my rent ;-) But I also like freedom to choose... > There are configuration settings in DT that are part of the way hardware is presented to > Linux and user-space, and have been for quite some time. We’ve been pretending they don’t > exist, but they are there… > As far as I know, a lot of that are older bindings, where more things just got applied, because it wasn't clear where DT will go. Regards, Steffen -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
