From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ludovic Desroches Subject: Re: [PATCH 2/4] of: DT quirks infrastructure Date: Fri, 20 Feb 2015 15:35:33 +0100 Message-ID: <20150220143533.GA29908@odux.rfo.atmel.com> References: <1424271576-1952-3-git-send-email-pantelis.antoniou@konsulko.com> <20150218154106.GC29429@leverpostej> <20150218173115.GG29429@leverpostej> <76BD1B22-BAED-4205-9B34-186907CE0217@konsulko.com> <54E613E7.2020405@gmail.com> <670D0881-DBF0-45E8-A502-A6DB2B77A750@konsulko.com> <54E61DD2.3060002@gmail.com> <53F2F94C-0C43-4A54-B8CD-EEC454A0AC19@konsulko.com> <54E742F2.80506@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <54E742F2.80506-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Hurley Cc: Pantelis Antoniou , frowand.list-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Tony Lindgren , Koen Kooi , Nicolas Ferre , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Grant Likely , Ludovic Desroches , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Matt Porter , Guenter Roeck List-Id: devicetree@vger.kernel.org On Fri, Feb 20, 2015 at 09:21:38AM -0500, Peter Hurley wrote: > On 02/19/2015 12:38 PM, Pantelis Antoniou wrote: > >=20 > >> On Feb 19, 2015, at 19:30 , Frank Rowand = wrote: > >> > >> On 2/19/2015 9:00 AM, Pantelis Antoniou wrote: > >>> Hi Frank, > >>> > >>>> On Feb 19, 2015, at 18:48 , Frank Rowand wrote: > >>>> > >>>> On 2/19/2015 6:29 AM, Pantelis Antoniou wrote: > >>>>> Hi Mark, > >>>>> > >>>>>> On Feb 18, 2015, at 19:31 , Mark Rutland wrote: > >>>>>> > >>>>>>>>> +While this may in theory work, in practice it is very cumb= ersome > >>>>>>>>> +for the following reasons: > >>>>>>>>> + > >>>>>>>>> +1. The act of selecting a different boot device tree blob = requires > >>>>>>>>> +a reasonably advanced bootloader with some kind of configu= ration or > >>>>>>>>> +scripting capabilities. Sadly this is not the case many ti= mes, the > >>>>>>>>> +bootloader is extremely dumb and can only use a single dt = blob. > >>>>>>>> > >>>>>>>> You can have several bootloader builds, or even a single bui= ld 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 b= oard. > >>>>>> > >>>>>> I wasn't on about the DTB. I was on about the loader binary, i= n 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 v= ariants > >>>>>> (albeit with limited utility) or the quirk approach wouldn't w= ork=E2=80=A6 > >>>>>> > >>>>> > >>>>> That=E2=80=99s not correct; the only part of the DTB that needs= to be common > >>>>> is the model property that would allow the quirk detection logi= c to fire. > >>>>> > >>>>> So, there is a base DTB that will work on all variants, but tha= t 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 sub= sets > >>>>> of the DTB that might work, they might be unsafe. > >>>>> > >>>>> For instance on the beaglebone the regulator configuration is d= ifferent > >>>>> between white and black, it is imperative you get them right ot= herwise > >>>>> you risk board damage. > >>>>> > >>>>>>>> So it's not necessarily true that you need a complex bootloa= der. > >>>>>>>> > >>>>>>> > >>>>>>>>> +2. On many instances boot time is extremely critical; in s= ome cases > >>>>>>>>> +there are hard requirements like having working video feed= s in under > >>>>>>>>> +2 seconds from power-up. This leaves an extremely small ti= me budget for > >>>>>>>>> +boot-up, as low as 500ms to kernel entry. The sanest way t= o get there > >>>>>>>>> +is by removing the standard bootloader from the normal boo= t sequence > >>>>>>>>> +altogether by having a very small boot shim that loads the= kernel and > >>>>>>>>> +immediately jumps to kernel, like falcon-boot mode in u-bo= ot does. > >>>>>>>> > >>>>>>>> Given my previous comments above I don't see why this is rel= evant. > >>>>>>>> You're already passing _some_ DTB here, so if you can organi= se for the > >>>>>>>> board to statically provide a sane DTB that's fine, or you c= an resort to > >>>>>>>> appended DTB if it's not possible to update the board config= uration. > >>>>>>>> > >>>>>>> > >>>>>>> You=E2=80=99re missing the point. I can=E2=80=99t use the sam= e DTB for each revision of the > >>>>>>> board. Each board is similar but it=E2=80=99s not identical. > >>>>>> > >>>>>> I think you've misunderstood my point. If you program the boar= d with the > >>>>>> relevant DTB, or use appended DTB, then you will pass the corr= ect DTB to > >>>>>> the kernel without need for quirks. > >>>>>> > >>>>>> I understand that each variant is somewhat incompatible (and h= ence needs > >>>>>> its own DTB). > >>>>> > >>>>> In theory it might work, in practice this does not. Ludovic men= tioned that they > >>>>> have 27 different DTBs in use at the moment. At a relatively co= mmon 60k per DTB > >>>>> that=E2=80=99s 27x60k =3D 1.6MB of DTBs, that need to be instal= led. > >>>> > >>>> < 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 secur= ity issue). > >>>> > >>>> I thought the DT blob was supposed to follow the same standard t= hat other OS's or > >>>> bootloaders understood. Are you willing to break that? (This i= s one of those > >>>> ripples I mentioned in my other emails.) > >>>> > >>> > >>> Trust no-one. > >>> > >>> This is one of those things that the kernel community doesn=E2=80= =99t 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 manufacturabili= ty. > >>> > >>> 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 m= illion? Guess what, > >>> instead of turning a profit you=E2=80=99re losing money if you on= ly have a few cents of profit > >>> per unit. > >> > >> I'm not installing physical components manually. Why would I be i= nstalling software > >> manually? (rhetorical question) > >> > >=20 > > Because on high volume product runs the flash comes preprogrammed a= nd is soldered as is. > >=20 > > Having a single binary to flash to every revision of the board make= s logistics considerably > > easier. > >=20 > > Having to boot and tweak the bootloader settings to select the corr= ect dtb (even if it=E2=80=99s present > > on the flash medium) takes time and is error-prone. > >=20 > > Factory time =3D=3D money, errors =3D=3D money. > >=20 > >>> > >>> No knobs to tweak means no knobs to break. And a broken knob can = have pretty bad consequences > >>> for a few million units.=20 > >> > >> And you produce a few million units before testing that the first = one off the line works? > >> > >=20 > > The first one off the line works. The rest will get some burn in an= d functional testing if you=E2=80=99re > > 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=E2=80=99re reasonably happy aft= er a little bit of statistical sampling. > >=20 > > Hardware is hard :) >=20 > I'm failing to see how this series improves your manufacturing proces= s at all. >=20 > 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 like= ly, you > have process control procedures in place so that you don't get 1 m= illion Blacks > flashed with the White eeprom image. >=20 > 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 ver= sa). >=20 > 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 Bl= acks; at > that point you're losing a lot more than a few cents of profit. An= d that has > nothing to do with what image you provided. >=20 As you said, we can imagine many reasons to have a failure during the production, having several DTB files will increase the risk. > 3. The factory is just as likely to use some other customer's image b= y accident, > so you're just as likely to have the same failure rate if you have= no test > process at the factory. >=20 > 4. If you're using offline programming, the image has to be tested af= ter > reflow anyway. >=20 > IOW, your QA process will not change at all =3D=3D same cost. >=20 > Regards, > Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe devicetree" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html