On 02/19/2016 06:25 PM, Peter Hurley wrote: > On 02/19/2016 02:42 AM, Aleksey Makarov wrote: >> Hi Peter, >> >> Thank you for review. >> >> On 02/19/2016 01:03 AM, Peter Hurley wrote: >>> On 02/17/2016 07:36 PM, Zheng, Lv wrote: >>>> Hi, >>>> >>>>> From: Aleksey Makarov [mailto:aleksey.makarov@xxxxxxxxxx] >>>>> Subject: Re: [PATCH v3 1/5] ACPI: change __init to __ref for >>>>> early_acpi_os_unmap_memory() >>>>> >>>>> Hi Lv, >>>>> >>>>> Thank you for review. >>>>> >>>>> On 02/17/2016 05:51 AM, Zheng, Lv wrote: >>>>> >>>>> [..] >>>>> >>>>>>>> early_acpi_os_unmap_memory() is marked as __init because it calls >>>>>>>> __acpi_unmap_table(), but only when acpi_gbl_permanent_mmap is not >>>>> set. >>>>>>>> >>>>>>>> acpi_gbl_permanent_mmap is set in __init acpi_early_init() >>>>>>>> so it is safe to call early_acpi_os_unmap_memory() from anywhere >>>>>>>> >>>>>>>> We need this function to be non-__init because we need access to >>>>>>>> some tables at unpredictable time--it may be before or after >>>>>>>> acpi_gbl_permanent_mmap is set. For example, SPCR (Serial Port Console >>>>>>>> Redirection) table is needed each time a new console is registered. >>>>>>>> It can be quite early (console_initcall) or when a module is inserted. >>>>>>>> When this table accessed before acpi_gbl_permanent_mmap is set, >>>>>>>> the pointer should be unmapped. This is exactly what this function >>>>>>>> does. >>>>>>> [Lv Zheng] >>>>>>> Why don't you use another API instead of early_acpi_os_unmap_memory() >>>>> in >>>>>>> case you want to unmap things in any cases. >>>>>>> acpi_os_unmap_memory() should be the one to match this purpose. >>>>>>> It checks acpi_gbl_ppermanent_mmap in acpi_os_unmap_iomem(). >>>>> >>>>> As far as I understand, there exist two steps in ACPI initialization: >>>>> >>>>> 1. Before acpi_gbl_permanent_mmap is set, tables received with >>>>> acpi_get_table_with_size() >>>>> are mapped by early_memremap(). If a subsystem gets such a pointer it >>>>> should be unmapped. >>>>> >>>>> 2 After acpi_gbl_permanent_mmap is set this pointer should not be unmapped >>>>> at all. >>>>> >>>> [Lv Zheng] >>>> This statement is wrong, this should be: >>>> As long as there is a __reference__ to the mapped table, the pointer should not be unmapped. >>>> In fact, we have a series to introduce acpi_put_table() to achieve this. >>>> So your argument is wrong from very first point. >>>> >>>>> That exactly what early_acpi_os_unmap_memory() does--it checks >>>>> acpi_gbl_permanent_mmap. >>>>> If I had used acpi_os_unmap_memory() after acpi_gbl_permanent_mmap had >>>>> been set, >>>>> it would have tried to free that pointer with an oops (actually, I checked that >>>>> and got that oops). >>>>> >>>>> So using acpi_os_unmap_memory() is not an option here, but >>>>> early_acpi_os_unmap_memory() >>>>> match perfectly. >>>> [Lv Zheng] >>>> I don't think so. >>>> For definition block tables, we know for sure there will always be references, until "Unload" opcode is invoked by the AML interpreter. >>>> But for the data tables, OSPMs should use them in this way: >>>> 1. map the table >>>> 2. parse the table and convert it to OS specific structures >>>> 3. unmap the table >>>> This helps to shrink virtual memory address space usages. >>>> >>>> So from this point of view, all data tables should be unmapped right after being parsed. >>>> Why do you need the map to be persistent in the kernel address space? >>>> You can always map a small table, but what if the table size is very big? >>>> >>>>> >>>>>>> And in fact early_acpi_os_unmap_memory() should be removed. >>>>> >>>>> I don't think so -- I have explained why. It does different thing. >>>>> Probably it (and/or other functions in that api) should be renamed. >>>>> >>>> [Lv Zheng] >>>> Just let me ask one more question. >>>> eary_acpi_os_unmap_memory() is not used inside of ACPICA. >>>> How ACPICA can work with just acpi_os_unmap_memory()? >>>> You can check drivers/acpi/tbxxx.c. >>>> Especially: acpi_tb_release_temp_table() and the code invoking it. >>>> >>>>>> [Lv Zheng] >>>>>> One more thing is: >>>>>> If you can't switch your driver to use acpi_os_unmap_memory() instead of >>>>> early_acpi_os_unmap_memory(), >>>>>> then it implies that your driver does have a defect. >>>>> >>>>> I still don't understand what defect, sorry. >>>> [Lv Zheng] >>>> If you can't ensure this sequence for using the data tables: >>>> 1. map the table >>>> 2. parse the table and convert it to OS specific structure >>>> 3. unmap the table >>>> It implies there is a bug in the driver or a bug in the ACPI subsystem core. >>> >>> Exactly. >>> >>> The central problem here is the way Aleksey is trying to hookup a console. >>> >>> What should be happening in this series is: >>> 1. early map SPCR >>> 2. parse the SPCR table >>> 3. call add_preferred_console() to add the SPCR console to the console table >>> 4. unmap SPCR >> >> This does not work. >> >> SPCR specifies address of the console, but add_preferred_console() accepts >> name of console and its index. There are no general method to translate address >> to name at such an early stage. > > > add_preferred_console(uart, 0, "io,0x3f8,115200"); First argument here should be (char *), the name of the console. We can not tell it just from the SPCR ACPI table without introducing new made up names and writting which/case that should be supported all the linux lifetime. I am also not quite shure I can tell the number of tty line (the 0 argument) just from the address. Did you mean "uart" here? As far as I can see, this would match the *earlycon*, not a regular console, that is not what this patch is about. It is about selecting regular (non-boot) consoles. I think translating address to string and then parsing it again is not unaceptable, but definitely worse than the approach in my patch, where I compare it directly. > This will start a console with the 8250 driver. I've already pointed > this out to you in an earlier review. This is what existing firmware > already does. > > This is also the method you will use to start an earlycon from the > DBG2 table, by additionally calling setup_earlycon(). > > >> There is another reason why I prefer to parse SPCR each time a console is registered. >> Some consoles can be registered very early in the initialization process and >> we have to be sure add_preferred_console() is called before that. > > However, since you're not adding a preferred console until uart driver > loads, there may already be a preferred console selected and running. > > This leads to weird issues like duplicated output on the serial console > when an earlycon is disabled by the dummy VGA/FB console then the > serial console starts and reprints the entire boot log on the same > terminal the earlycon already printed. Yes, misconfigured systems often misbehave. In this case I would question why there is an enabled console (we rely on ACPI to enable it). And I probably do not understand the scenario, but - "earlycon is disabled by the dummy VGA/FB console" and - "earlycon already printed" seem a bit contradictory. > Better just to parse both the DBG2 and SPCR tables before or at > early param, and add_preferred_consoles then. I still don't see why it's better, but I think I explained why it's worse. >> Of course, I could just parse it once and cache the results, but >> this still requires accessing SPCR before acpi_gbl_permanent_mmap >> is set *or* after that. >> >>> This trivial and unobtrusive method would already have a 8250 console >>> running via SPCR. I've already pointed this out in previous reviews. >>> >>> Further, the above method *will be required anyway* for the DBG2 table to >>> start an earlycon, which I've already pointed out in previous reviews. >>> >>> Then to enable amba-pl011 console via ACPI, add a console match() method >>> similar to the 8250 console match() method, univ8250_console_match(). >> >> So are you suggesting a separate method for each possible console? >> This is not acceptable. > > All 1 of them??? DBG2 specifies these subtypes of serial drivers: - Fully 16550-compatible - 16550 subset compatible with DBGP Revision 1 - ARM PL011 UART - (deprecated) ARM SBSA (2.x only) Generic UART supporting only 32-bit accesses - ARM SBSA Generic UART - ARM DCC - BCM2835 So it's at least 4 (or 3, I am not sure about ARM DCC) different types and the list is open. We would have to support it. > The 8250 driver already does this, so no work for you there. "uart" is for boot console, so it is not relevant. Or did you refer to something else? > That leaves you needing to write a trivial match() method for just > the amba-pl011 driver. Yes, that's probably OK, but in my series drivers should not be modified at all. I believe that's better. >> Do you suggest making up separate new name (like "uart" for 8250) for each type >> of conosole SPCR can specify? > > These are the documented names of the earlycons, which you'll be using > when you add the DGB2 table parsing. SPCR is not about earlycons. Thank you Aleksey Makarov >>> FWIW, PCI earlycon + console support was already submitted once before but >>> never picked up by GregKH. I think I'll just grab that and re-submit so >>> you would know what to emit for console options in the add_preferred_console(). >> >> Please do. Or just send a link to to that submission. > > Ok, will dig through and find it. > >> Do you mean the Leif Lindholm's patches: > > No. > >> https://lkml.kernel.org/g/1441716217-23786-1-git-send-email-leif.lindholm@xxxxxxxxxx >> >> He did same thing as I did in my v3 exept 1) he parses ACPI tree to match device >> (I just match SPCR against data that struct uart_port already has) >> 2) As you are suggesting, he parses SPCR once at a predefined point in initialization. >> And that's why his submission is RFC: he had troubles with the order of initialization. >> >> Thank you >> Aleksey Makarov >> >>> Regards, >>> Peter Hurley >>> >>> >>>>>> There is an early bootup requirement in Linux. >>>>>> Maps acquired during the early stage should be freed by the driver during the >>>>> early stage. >>>>>> And the driver should re-acquire the memory map after booting. >>>>> >>>>> Exactly. That's why I use early_acpi_os_unmap_memory(). The point is that >>>>> that code can be >>>>> called *before* acpi_gbl_permanent_mmap is set (at early initialization of for >>>>> example 8250 console) >>>>> or *after* acpi_gbl_permanent_mmap is set (at insertion of a module that >>>>> registers a console), >>>>> We just can not tell if the received table pointer should or sould not be freed >>>>> with early_memunmap() >>>>> (actually __acpi_unmap_table() or whatever) without checking >>>>> acpi_gbl_permanent_mmap, >>>>> but that's all too low level. >>>> [Lv Zheng] >>>> The driver should make sure that: >>>> Map/unmap is paired during early stage. >>>> For late stage, it should be another pair of map/unmap. >>>> >>>>> >>>>> Another option, as you describe, is to get this pointer early, don't free it >>>> [Lv Zheng] >>>> I mean you should free it early. >>>> >>>>> untill acpi_gbl_permanent_mmap is set, then free it (with >>>>> early_acpi_os_unmap_memory(), that's >>>>> ok because acpi_gbl_permanent_mmap is set in an init code), then get the >>>>> persistent >>>>> pointer to the table. The problem with it is that we can not just watch >>>>> acpi_gbl_permanent_mmap >>>>> to catch this exact moment. And also accessing acpi_gbl_permanent_mmap is >>>>> not good as it probably is >>>>> an implementation detail (i. e. too lowlevel) of the ACPI code. >>>>> Or I probably miss what you are suggesting. >>>>> >>>> [Lv Zheng] >>>> I mean, you should: >>>> During early stage: >>>> acpi_os_map_memory() >>>> Parse the table. >>>> acpi_os_unmap_memory(). >>>> >>>>>> This is because, during early bootup stage, there are only limited slots >>>>> available for drivers to map memory. >>>>>> So by changing __init to __ref here, you probably will hide many such defects. >>>>> >>>>> What defects? This funcions checks acpi_gbl_permanent_mmap. >>>>> BTW, exactly the same thing is done in the beginning of >>>>> acpi_os_unmap_memory() and than's ok, >>>>> that function is __ref. >>>>> >>>>>> And solving issues in this way doesn't seem to be an improvement. >>>>> >>>>> Could you please tell me where I am wrong? I still don't understand your point. >>>> [Lv Zheng] >>>> But anyway, the defect should be in ACPI subsystem core. >>>> The cause should be the API itself - acpi_get_table(). >>>> >>>> So I agree you can use early_acpi_os_unmap_memory() during the period the root causes are not cleaned up. >>>> But the bottom line is: the driver need to ensure that early_acpi_os_unmap_memory() is always invoked. >>>> As long as you can ensure this, I don't have objections for deploying early_acpi_os_unmap_memory() for now. >>>> >>>> Thanks and best regards >>>> -Lv >>>> >>>>> >>>>> Thank you >>>>> Aleksey Makarov >>>>> >>>>>> >>>>>> Thanks and best regards >>>>>> -Lv >>>>>> >>>>>>> >>>>>>> Thanks and best regards >>>>>>> -Lv >>>>>>> >>>>>>>> >>>>>>>> Signed-off-by: Aleksey Makarov <aleksey.makarov@xxxxxxxxxx> >>>>>>>> --- >>>>>>>> drivers/acpi/osl.c | 6 +++++- >>>>>>>> 1 file changed, 5 insertions(+), 1 deletion(-) >>>>>>>> >>>>>>>> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c >>>>>>>> index 67da6fb..8a552cd 100644 >>>>>>>> --- a/drivers/acpi/osl.c >>>>>>>> +++ b/drivers/acpi/osl.c >>>>>>>> @@ -497,7 +497,11 @@ void __ref acpi_os_unmap_memory(void *virt, >>>>>>>> acpi_size size) >>>>>>>> } >>>>>>>> EXPORT_SYMBOL_GPL(acpi_os_unmap_memory); >>>>>>>> >>>>>>>> -void __init early_acpi_os_unmap_memory(void __iomem *virt, acpi_size >>>>>>> size) >>>>>>>> +/* >>>>>>>> + * acpi_gbl_permanent_mmap is set in __init acpi_early_init() >>>>>>>> + * so it is safe to call early_acpi_os_unmap_memory() from anywhere >>>>>>>> + */ >>>>>>>> +void __ref early_acpi_os_unmap_memory(void __iomem *virt, acpi_size >>>>>>> size) >>>>>>>> { >>>>>>>> if (!acpi_gbl_permanent_mmap) >>>>>>>> __acpi_unmap_table(virt, size); >>>>>>>> -- >>>>>>>> 2.7.1 > > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
