Hi Peter, > On Feb 20, 2015, at 17:00 , Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote: > > On 02/20/2015 09:35 AM, Ludovic Desroches wrote: >> On Fri, Feb 20, 2015 at 09:21:38AM -0500, Peter Hurley wrote: >>> On 02/19/2015 12:38 PM, Pantelis Antoniou wrote: >>>> >>>>> On Feb 19, 2015, at 19:30 , Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>>>> >>>>> On 2/19/2015 9:00 AM, Pantelis Antoniou wrote: >>>>>> Hi Frank, >>>>>> >>>>>>> On Feb 19, 2015, at 18:48 , Frank Rowand <frowand.list@xxxxxxxxx> wrote: >>>>>>> >>>>>>> On 2/19/2015 6:29 AM, Pantelis Antoniou wrote: >>>>>>>> Hi Mark, >>>>>>>> >>>>>>>>> On Feb 18, 2015, at 19:31 , Mark Rutland <mark.rutland@xxxxxxx> wrote: >>>>>>>>> >>>>>>>>>>>> +While this may in theory work, in practice it is very cumbersome >>>>>>>>>>>> +for the following reasons: >>>>>>>>>>>> + >>>>>>>>>>>> +1. The act of selecting a different boot device tree blob requires >>>>>>>>>>>> +a reasonably advanced bootloader with some kind of configuration or >>>>>>>>>>>> +scripting capabilities. Sadly this is not the case many times, the >>>>>>>>>>>> +bootloader is extremely dumb and can only use a single dt blob. >>>>>>>>>>> >>>>>>>>>>> You can have several bootloader builds, or even a single build with >>>>>>>>>>> something like appended DTB to get an appropriate DTB if the same binary >>>>>>>>>>> will otherwise work across all variants of a board. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> No, the same DTB will not work across all the variants of a board. >>>>>>>>> >>>>>>>>> I wasn't on about the DTB. I was on about the loader binary, in the case >>>>>>>>> the FW/bootloader could be common even if the DTB couldn't. >>>>>>>>> >>>>>>>>> To some extent there must be a DTB that will work across all variants >>>>>>>>> (albeit with limited utility) or the quirk approach wouldn't work… >>>>>>>>> >>>>>>>> >>>>>>>> That’s not correct; the only part of the DTB that needs to be common >>>>>>>> is the model property that would allow the quirk detection logic to fire. >>>>>>>> >>>>>>>> So, there is a base DTB that will work on all variants, but that only means >>>>>>>> that it will work only up to the point that the quirk detector method >>>>>>>> can work. So while in recommended practice there are common subsets >>>>>>>> of the DTB that might work, they might be unsafe. >>>>>>>> >>>>>>>> For instance on the beaglebone the regulator configuration is different >>>>>>>> between white and black, it is imperative you get them right otherwise >>>>>>>> you risk board damage. >>>>>>>> >>>>>>>>>>> So it's not necessarily true that you need a complex bootloader. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>>>> +2. On many instances boot time is extremely critical; in some cases >>>>>>>>>>>> +there are hard requirements like having working video feeds in under >>>>>>>>>>>> +2 seconds from power-up. This leaves an extremely small time budget for >>>>>>>>>>>> +boot-up, as low as 500ms to kernel entry. The sanest way to get there >>>>>>>>>>>> +is by removing the standard bootloader from the normal boot sequence >>>>>>>>>>>> +altogether by having a very small boot shim that loads the kernel and >>>>>>>>>>>> +immediately jumps to kernel, like falcon-boot mode in u-boot does. >>>>>>>>>>> >>>>>>>>>>> Given my previous comments above I don't see why this is relevant. >>>>>>>>>>> You're already passing _some_ DTB here, so if you can organise for the >>>>>>>>>>> board to statically provide a sane DTB that's fine, or you can resort to >>>>>>>>>>> appended DTB if it's not possible to update the board configuration. >>>>>>>>>>> >>>>>>>>>> >>>>>>>>>> You’re missing the point. I can’t use the same DTB for each revision of the >>>>>>>>>> board. Each board is similar but it’s not identical. >>>>>>>>> >>>>>>>>> I think you've misunderstood my point. If you program the board with the >>>>>>>>> relevant DTB, or use appended DTB, then you will pass the correct DTB to >>>>>>>>> the kernel without need for quirks. >>>>>>>>> >>>>>>>>> I understand that each variant is somewhat incompatible (and hence needs >>>>>>>>> its own DTB). >>>>>>>> >>>>>>>> In theory it might work, in practice this does not. Ludovic mentioned that they >>>>>>>> have 27 different DTBs in use at the moment. At a relatively common 60k per DTB >>>>>>>> that’s 27x60k = 1.6MB of DTBs, that need to be installed. >>>>>>> >>>>>>> < snip > >>>>>>> >>>>>>> Or you can install the correct DTB on the board. You trust your manufacturing line >>>>>>> to install the correct resistors. You trust your manufacturing line to install the >>>>>>> correct kernel version (eg an updated version to resolve a security issue). >>>>>>> >>>>>>> I thought the DT blob was supposed to follow the same standard that other OS's or >>>>>>> bootloaders understood. Are you willing to break that? (This is one of those >>>>>>> ripples I mentioned in my other emails.) >>>>>>> >>>>>> >>>>>> Trust no-one. >>>>>> >>>>>> This is one of those things that the kernel community doesn’t understand which makes people >>>>>> who push product quite mad. >>>>>> >>>>>> Engineering a product is not only about meeting customer spec, in order to turn a profit >>>>>> the whole endeavor must be engineered as well for manufacturability. >>>>>> >>>>>> Yes, you can always manually install files in the bootloader. For 1 board no problem. >>>>>> For 10 doable. For 100 I guess you can hire an extra guy. For 1 million? Guess what, >>>>>> instead of turning a profit you’re losing money if you only have a few cents of profit >>>>>> per unit. >>>>> >>>>> I'm not installing physical components manually. Why would I be installing software >>>>> manually? (rhetorical question) >>>>> >>>> >>>> Because on high volume product runs the flash comes preprogrammed and is soldered as is. >>>> >>>> Having a single binary to flash to every revision of the board makes logistics considerably >>>> easier. >>>> >>>> Having to boot and tweak the bootloader settings to select the correct dtb (even if it’s present >>>> on the flash medium) takes time and is error-prone. >>>> >>>> Factory time == money, errors == money. >>>> >>>>>> >>>>>> No knobs to tweak means no knobs to break. And a broken knob can have pretty bad consequences >>>>>> for a few million units. >>>>> >>>>> And you produce a few million units before testing that the first one off the line works? >>>>> >>>> >>>> The first one off the line works. The rest will get some burn in and functional testing if you’re >>>> lucky. In many cases where the product is very cheap it might make financial sense to just ship >>>> as is and deal with recalls, if you’re reasonably happy after a little bit of statistical sampling. >>>> >>>> Hardware is hard :) >>> >>> I'm failing to see how this series improves your manufacturing process at all. >>> >>> 1. Won't you have to provide the factory with different eeprom images for the >>> White and Black? You _trust_ them to get that right, or more likely, you >>> have process control procedures in place so that you don't get 1 million Blacks >>> flashed with the White eeprom image. >>> >>> 2. The White and Black use different memory technology so it's not as if the >>> eMMC from the Black will end up on the White SMT line (or vice versa). >>> >>> 3 For that matter, why wouldn't you worry that all the microSD cards intended >>> for the White were accidentally assembled with the first 50,000 Blacks; at >>> that point you're losing a lot more than a few cents of profit. And that has >>> nothing to do with what image you provided. >>> >> >> As you said, we can imagine many reasons to have a failure during the >> production, having several DTB files will increase the risk. > > It's interesting that you don't see the added complexity of open-coding > the i2c driver or mixing DTS fragments for different designs as increased risk > (for us all). > > You don’t have to use it. Some people really do though. As for increased risk I expect to see arguments instead of a statement. >>> 3. The factory is just as likely to use some other customer's image by accident, >>> so you're just as likely to have the same failure rate if you have no test >>> process at the factory. >>> >>> 4. If you're using offline programming, the image has to be tested after >>> reflow anyway. >>> >>> IOW, your QA process will not change at all == same cost. >>> >>> Regards, >>> Peter Hurley > Regards — Pantelis -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
