| Message ID | 20240502-mips_debug_ll-v3-0-3b61f30e484c@flygoat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | MIPS: Unify low-level debugging functionalities | expand |
在2024年5月2日五月 上午10:59，Jiaxun Yang写道： > Hi all, > > This is a attempt to bring all low-level debugging print functions > together and provide a arm-like low-level debugging interface and > a further capability to debug early exceptions. > > This patch elimiate platform specific early_printk, zboot printing > functions and cps-vec-ns16550 by newly introduced debug_ll. > > Hope you'll find them handy :-) > > Happy hacking! > > Thanks > > Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com> A gentle ping. Our reviewing capacity is quite low recently, hope everything is fine with Thomas. Thanks [...] - Jiaxun
在2024年5月15日五月 下午10:28，Jiaxun Yang写道： [...] > > A gentle ping. > > Our reviewing capacity is quite low recently, hope everything is fine > with Thomas. Another gentle-ish ping after 6.10 merge window. This series has been floating here for so long, if I missed the merge window, I think I deserve a notice. Thanks > > Thanks > [...] > - Jiaxun
On Wed, May 22, 2024 at 08:15:22AM +0100, Jiaxun Yang wrote: > > > 在2024年5月15日五月 下午10:28，Jiaxun Yang写道： > [...] > > > > A gentle ping. > > > > Our reviewing capacity is quite low recently, hope everything is fine > > with Thomas. > > Another gentle-ish ping after 6.10 merge window. > > This series has been floating here for so long, if I missed the merge > window, I think I deserve a notice. hmmm, I thought I was clear enough on version 1 of this series. I don't want an additional printk like debug interface, There is prom_putchar() and early printk console, which always got me past any boot issue. Thomas.
在2024年5月22日五月 上午9:03，Thomas Bogendoerfer写道： [...] > > hmmm, I thought I was clear enough on version 1 of this series. > > I don't want an additional printk like debug interface, There is > prom_putchar() and early printk console, which always got me past > any boot issue. So it's not an additional printk like debug interface, it actually merged 3 existing debug interfaces, the first being zboot's assembly print routines, the second being CPS's assembly print routines, the third being some platform specific early printk. I think they are all essential for debugging early faults, for zboot that's the only way to print something at decompressing stage, for CPS as other cores are booting in non-coherent state we can't safely use any kernel functions, for early_printk that can help us *reduce* the amount of early printk code by just adding UART base to config. The only thing being added is the ability to debug very early exception, even that is partially ported from existing CPS assembly debugging routines. Please let me know your thoughts. Thanks > > Thomas. > > -- > Crap can work. Given enough thrust pigs will fly, but it's not necessarily a > good idea. [ RFC1925, 2.3 ]
在2024年5月22日五月 上午9:28，Jiaxun Yang写道： > 在2024年5月22日五月 上午9:03，Thomas Bogendoerfer写道： > [...] >> >> hmmm, I thought I was clear enough on version 1 of this series. >> >> I don't want an additional printk like debug interface, There is >> prom_putchar() and early printk console, which always got me past >> any boot issue. > > So it's not an additional printk like debug interface, it actually > merged 3 existing debug interfaces, the first being zboot's assembly > print routines, the second being CPS's assembly print routines, the > third being some platform specific early printk. I think they are > all essential for debugging early faults, for zboot that's the only > way to print something at decompressing stage, for CPS as other cores > are booting in non-coherent state we can't safely use any kernel > functions, for early_printk that can help us *reduce* the amount > of early printk code by just adding UART base to config. > > The only thing being added is the ability to debug very early exception, > even that is partially ported from existing CPS assembly debugging routines. > > Please let me know your thoughts. That being said, have you noticed that prom_putchar and early_printk is a non-extant on generic mach, ingenic, ralink etc? That's because we really don't want to introduce any platform specific UART code for early debugging on new platforms. With DEBUG_LL introduced by Arm it's only a Kconfig option to do the trick. I've got review tags in PATCH v2, that means not only me feeling that this series is reasonable. arm64 / riscv doesn't need that because they are well standardized and it's almost guaranteed that kernel can boot into earlycon without much drama. For MIPS that's not the case, there are too many things that may go wrong, from zboot decompressor to cpu-probe and memblock. We really lacks a way to debug things early, we need something that is available at 1st instruction at kernel entry. Furthermore, many MIPS processors don't come with JTAG or alike debugging support, that makes debugging even harder, there is no way to debug an early exception if your firmware doesn't handle it. That's all the motivation behind the series. Besides, I think our communication needs to be improved. At PATCH v1 you made your point in reply, that's fair. So I also replied twice for clarification. I heard nothing back, so I assume you want to see how would it develop to address your concern. Then I posted PATCH v2 and v3 to further improve the series, after that I pinged twice on PATCH v3. That's in a 6-month timeframe with multiple transactions, you need to inform us your intention, even if it's a NAK or you don't want to engage on this topic further. Quoting the maintainer handbook [1]: "If the review process or validation for a particular change will take longer than the expected review timeline for the subsystem, maintainer should reply to the submission indicating that the work is being done, and when to expect full results." Radio silence won't help anything, it's wasting time for both of us. Please, give a shout if it's possible. I can see some other series being slipped away this way, like I6500 multi-cluster patch, which is sent even earlier and respined many times over. I can recall Mobileye series had a hard time on getting your attention, luckily we went through it. Quoting the maintainer handbook [1]: "Nonetheless when the work does arrive (in form of patches which need review, user bug reports etc.) it has to be acted upon promptly.". I understand Linux/MIPS is not your day job, also you need to take breaks or go on holidays. Sometimes you may burn out from your maintainer duties. That's fine, we are all human beings. I'm not expecting a 1-week SLA or something, but 6 months or longer to expect an action is appalling to me. I'd strongly recommend you to look for a secondary maintainer, as mentioned in maintainer handbook [1]: "Modern best practices dictate that there should be at least two maintainers for any piece of code, no matter how trivial". I understand you reject the idea once when Paul handed maintainership to you, but there are clear evidences to show that something needs to be done. You might need a hand on handling stuff promptly and understanding some modern MIPS stuff. I have many, many tiny improvements to MIPS kernel locally. Furthermore, I do bring-up for both new and ancient MIPS systems. I never got a chance to send them out because I want you prioritise on those fundamental series. Apologise for potential aggressive tone in this email. I just can't clam down when I think back about your reply, and I think we really need to talk about it. Thanks [1]: https://docs.kernel.org/maintainer/feature-and-driver-maintainers.html
On Wed, 22 May 2024, Jiaxun Yang wrote: > That being said, have you noticed that prom_putchar and early_printk is > a non-extant on generic mach, ingenic, ralink etc? That's because we > really don't want to introduce any platform specific UART code for > early debugging on new platforms. With DEBUG_LL introduced by Arm it's > only a Kconfig option to do the trick. IMHO that is however the logical thing to do. And then you need no magic options to fiddle with and say a distribution kernel will dump whatever it has to say if something wrong has happened early on. IOW just wire `prom_putchar' as required, using C code preferably. NB YAMON does have a `print' entry point for console output, so for the Malta platform you can trivially use just that, no need for messy ad hoc 8250 code. As to intercepting exceptions, it depends. Again YAMON does handle that and dumps the register state, so with the Malta you get the information required. For less capable ones it might make sense, but it ISTM like a candidate for an independent change, and then again I fail to see why the handler has to be written in the assembly language rather than C. Maciej
在2024年5月26日五月 下午1:44，Maciej W. Rozycki写道： > On Wed, 22 May 2024, Jiaxun Yang wrote: > >> That being said, have you noticed that prom_putchar and early_printk is >> a non-extant on generic mach, ingenic, ralink etc? That's because we >> really don't want to introduce any platform specific UART code for >> early debugging on new platforms. With DEBUG_LL introduced by Arm it's >> only a Kconfig option to do the trick. Hi Maciej, Thanks for your thoughts, my two cents below. > > IMHO that is however the logical thing to do. And then you need no magic > options to fiddle with and say a distribution kernel will dump whatever it > has to say if something wrong has happened early on. This is a strict debug only options, we are not expecting any distribution kernel to enable it. It has made itself explicit that no production device should enable it. Setting UART address for debug console by developers know what are they doing is a proven approach among multiple places in multiple projects. For kernel we have general earlycon cmdline option that would take MMIO base address, Arm's DEBUG_LL had taken a similar approach and U-Boot have CONFIG_DEBUG_UART_BASE, even our old zboot debug print code is taking such approach. It takes a balance between platform dependent code addition and bring-up debugging capability. I fail to see why does it suddenly become an undesired thing here. > > IOW just wire `prom_putchar' as required, using C code preferably. NB > YAMON does have a `print' entry point for console output, so for the Malta > platform you can trivially use just that, no need for messy ad hoc 8250 > code. Sadly for the majority of modern MIPS devices are dominated by U-Boot or vendor's simple loader. In most cases, runtime APIs are not provided by default. Even if it's enabled, there are still a couple of reasons preventing it to be utilized properly. U-Boot relies on global pointer stored in K0 to save global runtime data, kernel will clobber it very early and makes U-Boot non-functional. On devices with limited memory, it's easy to get U-Boot memory being clobbered by kernel and render U-Boot's runtime useless anyway. That's why many new-ish platforms such as lantiq brings it's own UART implementations for prom_putchar. However, for generic platform implementing prom_putchar means we need to introduce platform dependent code, which we had to pay all the price to avoid. We have many in-tree and out-of tree generic platform users who don't need to add any single line of code to bring up their platform, thanks to DeviceTree, but they still need something to help with debugging bring up process when devicetree went wrong or early panics. > > As to intercepting exceptions, it depends. Again YAMON does handle that > and dumps the register state, so with the Malta you get the information > required. For less capable ones it might make sense, but it ISTM like a > candidate for an independent change, and then again I fail to see why the > handler has to be written in the assembly language rather than C. Again for U-Boot debug exception dumping is optional and I know many devices not shipping with that enabled. Even if it's enabled, it will stop to work after U-Boot's memory/global pointer being clobbered or ebase being overridden by kernel. Not to mention that Bootloader's exception dumping won't work with CPS secondary cores. Paul wrote cps-vec.S and cps-vec-ns16550.S in pure assembly for reasons. Stack pointer is not initialized at second core & we really want to reduce code footprint on secondary core to minimize side effects before coherence is enabled. When the infra is here, expand it to generic early exception is just tens of lines. I fail to see the reason to bring in hundreds lines of C code for the same functionality. > > Maciej Although it's a pure technical discussion, I still want to expand that while I appreciate what you have done to the MIPS, sometimes I feel like we are not on the same page because you guys are away from frontliner for so long and missed many contexts. MIPS is still evolving, although I never appeared here with my corp email, I'm one of those behind the scene. I draft new architecture specs, write AVP and internal simulators, do RTL coding for future core products, helping customers design SoC products, design software architecture and bringing them up. I kept FOSS as my hobby and I tried my best to keep upstream in sync with modern practices. I love MIPS heritages, I own an SGI Indy and Algorithmics P-4032, I made some fixes on MAME emulator for indy to keep kernel running on it. I'm still frequently fascinated by those brilliant old designs. But I think we still need to make progress. While maintaining compatibility with all those old things, we need to adopt common practices that have been proven by other architectures and make our own innovations. We need to make the development process agile, so no developer is turned away. We need to adopt modern booting protocols like EFI and ensure generic kernel is really generic and not being diverted because of different loading address.... I don't know if you would agree with my in both technical details and ideology, but I think it's the time to make my intention clear. Thanks
Hi all, This is a attempt to bring all low-level debugging print functions together and provide a arm-like low-level debugging interface and a further capability to debug early exceptions. This patch elimiate platform specific early_printk, zboot printing functions and cps-vec-ns16550 by newly introduced debug_ll. Hope you'll find them handy :-) Happy hacking! Thanks Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com> --- Changes in v3: - Collect review tags - Fix an indentation - Link to v2: https://lore.kernel.org/r/20240326-mips_debug_ll-v2-0-b64abc76f2a1@flygoat.com --- Jiaxun Yang (9): MIPS: asm: Move strings to .rodata.str section MIPS: debug: Implement low-level debugging functions MIPS: debug: Hook up DEBUG_LL with early printk MIPS: debug: Provide an early exception vector for low-level debugging MIPS: debug_ll: Add Kconfig symbols for some 8250 uarts MIPS: debug_ll: Implement support for Alchemy uarts MIPS: debug_ll: Implement support for AR933X uarts MIPS: zboot: Convert to use debug_ll facilities MIPS: CPS: Convert to use debug_ll facilities arch/mips/Kconfig | 12 +- arch/mips/Kconfig.debug | 240 +++++++++++++++++++++++-------- arch/mips/boot/compressed/Makefile | 9 +- arch/mips/boot/compressed/dbg.c | 39 ----- arch/mips/boot/compressed/debug-vec.S | 3 + arch/mips/boot/compressed/debug.S | 3 + arch/mips/boot/compressed/decompress.h | 8 +- arch/mips/boot/compressed/head.S | 6 + arch/mips/boot/compressed/uart-16550.c | 49 ------- arch/mips/boot/compressed/uart-alchemy.c | 9 -- arch/mips/boot/compressed/uart-ath79.c | 2 - arch/mips/boot/compressed/uart-prom.c | 9 -- arch/mips/include/asm/asm.h | 2 +- arch/mips/include/debug/8250.S | 60 ++++++++ arch/mips/include/debug/alchemy.S | 46 ++++++ arch/mips/include/debug/ar933x.S | 41 ++++++ arch/mips/include/debug/uhi.S | 48 +++++++ arch/mips/kernel/Makefile | 4 +- arch/mips/kernel/cps-vec.S | 16 +-- arch/mips/kernel/debug-vec.S | 194 +++++++++++++++++++++++++ arch/mips/kernel/debug.S | 130 +++++++++++++++++ arch/mips/kernel/early_printk.c | 19 +++ arch/mips/kernel/head.S | 4 + 23 files changed, 756 insertions(+), 197 deletions(-) --- base-commit: 084c8e315db34b59d38d06e684b1a0dd07d30287 change-id: 20240326-mips_debug_ll-ce72fee1b6a2 Best regards,