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    SubjectRe: [PATCH] i2c: i801: Register optional lis3lv02d i2c device on Dell machines
    On Tue, Jan 03, 2017 at 09:39:13PM +0100, Pali Rohár wrote:
    > On Tuesday 03 January 2017 21:24:18 Dmitry Torokhov wrote:
    > > On Tue, Jan 03, 2017 at 09:05:51PM +0100, Pali Rohár wrote:
    > > > On Tuesday 03 January 2017 20:48:12 Dmitry Torokhov wrote:
    > > > > On Tue, Jan 03, 2017 at 07:50:17PM +0100, Pali Rohár wrote:
    > > > > > On Tuesday 03 January 2017 19:38:43 Dmitry Torokhov wrote:
    > > > > > > On Tue, Jan 03, 2017 at 10:06:41AM +0100, Benjamin Tissoires
    > > > > > >
    > > > > > > wrote:
    > > > > > > > On Dec 29 2016 or thereabouts, Pali Rohár wrote:
    > > > > > > > > On Thursday 29 December 2016 22:09:32 Michał Kępień wrote:
    > > > > > > > > > > On Thursday 29 December 2016 14:47:19 Michał Kępień
    > > > > > > > > > > wrote:
    > > > > > > > > > > > > On Thursday 29 December 2016 09:29:36 Michał
    > > > > > > > > > > > > Kępień
    > > > > > > > > > > > >
    > > > > > > > > > > > > wrote:
    > > > > > > > > > > > > > > Dell platform team told us that some (DMI
    > > > > > > > > > > > > > > whitelisted) Dell Latitude machines have ST
    > > > > > > > > > > > > > > microelectronics accelerometer at i2c address
    > > > > > > > > > > > > > > 0x29. That i2c address is not specified in
    > > > > > > > > > > > > > > DMI or ACPI, so runtime detection without
    > > > > > > > > > > > > > > whitelist which is below is not possible.
    > > > > > > > > > > > > > >
    > > > > > > > > > > > > > > Presence of that ST microelectronics
    > > > > > > > > > > > > > > accelerometer is verified by existence of
    > > > > > > > > > > > > > > SMO88xx ACPI device which represent that
    > > > > > > > > > > > > > > accelerometer. Unfortunately without i2c
    > > > > > > > > > > > > > > address.
    > > > > > > > > > > > > >
    > > > > > > > > > > > > > This part of the commit message sounded a bit
    > > > > > > > > > > > > > confusing to me at first because there is
    > > > > > > > > > > > > > already an ACPI driver which handles SMO88xx
    > > > > > > > > > > > > >
    > > > > > > > > > > > > > devices (dell-smo8800). My understanding is
    > > > > > > > > > > > > > that:
    > > > > > > > > > > > > > * the purpose of this patch is to expose a
    > > > > > > > > > > > > > richer interface (as
    > > > > > > > > > > > > >
    > > > > > > > > > > > > > provided by lis3lv02d) to these devices on
    > > > > > > > > > > > > > some machines,
    > > > > > > > > > > > > >
    > > > > > > > > > > > > > * on whitelisted machines, dell-smo8800 and
    > > > > > > > > > > > > > lis3lv02d can work
    > > > > > > > > > > > > >
    > > > > > > > > > > > > > simultaneously (even though dell-smo8800
    > > > > > > > > > > > > > effectively duplicates the work that
    > > > > > > > > > > > > > lis3lv02d does).
    > > > > > > > > > > > >
    > > > > > > > > > > > > No. dell-smo8800 reads from ACPI irq number and
    > > > > > > > > > > > > exports /dev/freefall device which notify
    > > > > > > > > > > > > userspace about falls. lis3lv02d is i2c driver
    > > > > > > > > > > > > which exports axes of accelerometer. Additionaly
    > > > > > > > > > > > > lis3lv02d can export also /dev/freefall if
    > > > > > > > > > > > > registerer of i2c device provides irq number --
    > > > > > > > > > > > > which is not case of this patch.
    > > > > > > > > > > > >
    > > > > > > > > > > > > So both drivers are doing different things and
    > > > > > > > > > > > > both are useful.
    > > > > > > > > > > > >
    > > > > > > > > > > > > IIRC both dell-smo8800 and lis3lv02d represent
    > > > > > > > > > > > > one HW device (that ST microelectronics
    > > > > > > > > > > > > accelerometer) but due to complicated HW
    > > > > > > > > > > > > abstraction and layers on Dell laptops it is
    > > > > > > > > > > > > handled by two drivers, one ACPI and one i2c.
    > > > > > > > > > > > >
    > > > > > > > > > > > > Yes, in ideal world irq number should be passed
    > > > > > > > > > > > > to lis3lv02d driver and that would export whole
    > > > > > > > > > > > > device (with /dev/freefall too), but due to HW
    > > > > > > > > > > > > abstraction it is too much complicated...
    > > > > > > > > > > >
    > > > > > > > > > > > Why? AFAICT, all that is required to pass that IRQ
    > > > > > > > > > > > number all the way down to lis3lv02d is to set the
    > > > > > > > > > > > irq field of the struct i2c_board_info you are
    > > > > > > > > > > > passing to i2c_new_device(). And you can extract
    > > > > > > > > > > > that IRQ number e.g. in
    > > > > > > > > > > > check_acpi_smo88xx_device(). However, you would
    > > > > > > > > > > > then need to make sure dell-smo8800 does not
    > > > > > > > > > > > attempt to request the same IRQ on whitelisted
    > > > > > > > > > > > machines. This got me thinking about a way to
    > > > > > > > > > > > somehow incorporate your changes into dell-smo8800
    > > > > > > > > > > > using Wolfram's bus_notifier suggestion, but I do
    > > > > > > > > > > > not have a working solution for now. What is
    > > > > > > > > > > > tempting about this approach is that you would not
    > > > > > > > > > > > have to scan the ACPI namespace in search of
    > > > > > > > > > > > SMO88xx devices, because smo8800_add() is
    > > > > > > > > > > > automatically called for them. However, I fear that
    > > > > > > > > > > > the resulting solution may be more complicated than
    > > > > > > > > > > > the one you submitted.
    > > > > > > > > > >
    > > > > > > > > > > Then we need to deal with lot of problems. Order of
    > > > > > > > > > > loading .ko modules is undefined. Binding devices to
    > > > > > > > > > > drivers registered by .ko module is also in "random"
    > > > > > > > > > > order. At any time any of those .ko module can be
    > > > > > > > > > > unloaded or at least device unbind (via sysfs) from
    > > > > > > > > > > driver... And there can be some pathological
    > > > > > > > > > > situation (thanks to adding ACPI layer as Andy
    > > > > > > > > > > pointed) that there will be more SMO88xx devices in
    > > > > > > > > > > ACPI. Plus you can compile kernel with and without
    > > > > > > > > > > those modules and also you can blacklist loading
    > > > > > > > > > > them (so compile time check is not enough). And
    > > > > > > > > > > still some correct message notifier must be used.
    > > > > > > > > > >
    > > > > > > > > > > I think such solution is much much more complicated,
    > > > > > > > > > > there are lot of combinations of kernel configuration
    > > > > > > > > > > and available dell devices...
    > > > > > > > > >
    > > > > > > > > > I tried a few more things, but ultimately failed to
    > > > > > > > > > find a nice way to implement this.
    > > > > > > > > >
    > > > > > > > > > Another issue popped up, though. Linus' master branch
    > > > > > > > > > contains a recent commit by Benjamin Tissoires (CC'ed),
    > > > > > > > > > 4d5538f5882a ("i2c: use an IRQ to report Host Notify
    > > > > > > > > > events, not alert") which breaks your patch. The
    > > > > > > > > > reason for that is that lis3lv02d relies on the i2c
    > > > > > > > > > client's IRQ being 0 to detect that it should not
    > > > > > > > > > create /dev/freefall.
    > > > > > > > > >
    > > > > > > > > > Benjamin's patch causes the Host Notify IRQ to be
    > > > > > > > > >
    > > > > > > > > > assigned to the i2c client your patch creates, thus
    > > > > > > > > > causing lis3lv02d to create /dev/freefall, which in
    > > > > > > > > > turn conflicts with dell-smo8800 which is trying to
    > > > > > > > > > create /dev/freefall itself.
    > > > > > > > >
    > > > > > > > > So 4d5538f5882a is breaking lis3lv02d driver...
    > > > > > > >
    > > > > > > > Apologies for that.
    > > > > > > >
    > > > > > > > I could easily fix this by adding a kernel API to know
    > > > > > > > whether the provided irq is from Host Notify or if it was
    > > > > > > > coming from an actual declaration. However, I have no idea
    > > > > > > > how many other drivers would require this (hopefully only
    > > > > > > > this one).
    > > > > > > >
    > > > > > > > One other solution would be to reserve the Host Notify IRQ
    > > > > > > > and let the actual drivers that need it to set it, but
    > > > > > > > this was not the best solution according to Dmitri. On my
    > > > > > > > side, I am not entirely against this given that it's a
    > > > > > > > chip feature, so the driver should be able to know that
    > > > > > > > it's available.
    > > > > > > >
    > > > > > > > Dmitri, Wolfram, Jean, any preferences?
    > > > > > >
    > > > > > > I read this:
    > > > > > >
    > > > > > > "IIRC both dell-smo8800 and lis3lv02d represent one HW device
    > > > > > > (that ST microelectronics accelerometer) but due to
    > > > > > > complicated HW abstraction and layers on Dell laptops it is
    > > > > > > handled by two drivers, one ACPI and one i2c."
    > > > > > >
    > > > > > > and that is the core of the issue. You have 2 drivers
    > > > > > > fighting over the same device. Fix this and it will all
    > > > > > > work.
    > > > > >
    > > > > > With my current implementation (which I sent in this patch),
    > > > > > they are not fighting.
    > > > > >
    > > > > > dell-smo8800 exports /dev/freefall (and nothing more) and
    > > > > > lis3lv02d only accelerometer device as lis3lv02d driver does
    > > > > > not get IRQ number in platform data.
    > > > > >
    > > > > > > As far as I can see hp_accel instantiates lis3lv02d and
    > > > > > > accesses it via ACPI methods, can the same be done for Dell?
    > > > > >
    > > > > > No, Dell does not have any ACPI methods. And as I wrote in ACPI
    > > > > > or DMI is even not i2c address of device, so it needs to be
    > > > > > specified in code itself.
    > > > > >
    > > > > > Really there is no other way... :-(
    > > > >
    > > > > Sure there is:
    > > > >
    > > > > 1. dell-smo8800 instantiates I2C device as "dell-smo8800-accel".
    > > > > 2. dell-smo8800 provides read/write functions for lis3lv02d that
    > > > > simply forward requests to dell-smo8800-accel i2c client.
    > > > > 3. dell-smo8800 instantiates lis3lv02d instance like hp_accel
    > > > > does.
    > > >
    > > > Sorry, but I do not understand how you mean it... Why to provides
    > > > new read/write i2c functions which are already implemented by
    > > > i2c-i801 bus and lis3lv02d i2c driver?
    > >
    > > Because that would allow you to avoid clashes with i2c creating
    > > interrupt mapping for client residing on host-notify-capable
    > > controller.
    > >
    > > > > Alternatively, can lis3lv02d be tasked to create /dev/freefall?
    > > >
    > > > If i2c_board_info contains IRQ then lis3lv02d create /dev/freefall
    > > > device.
    > > >
    > > > But... what is problem with current implementation? Accelerometer
    > > > HW provides two functions:
    > > >
    > > > 1) 3 axes reports
    > > > 2) Disk freefall detection
    > > >
    > > > And 1) is handled by i2c driver lis3lv02d and 2) is by
    > > > dell-smo8800. Both functions are independent here.
    > > >
    > > > I think you just trying to complicate this situation even more to
    > > > be more complicated as currently is.
    > >
    > > Because this apparently does not work for you, does it?
    >
    > It is working fine. I do not see any problem.
    >
    > > In general,
    > > if you want the same hardware be handled by 2 different drivers you
    > > are going to have bad time.
    >
    > Yes, but in this case half of device is ACPI based and other half i2c
    > based. This is problem of ACPI and Dell design.
    >
    > > It seems to be that /dev/freefall in dell-smo8800 and lis3lv02d are
    > > the same, right?
    >
    > Yes. I understand that clean solution is to have one driver which
    > provides everything.
    >
    > But because half of data are ACPI and half i2c, you still needs to
    > create two drivers (one ACPI and one i2c). You can put both drivers into
    > one .ko module, but still these will be two drivers due to how ACPI and
    > i2c linux abstractions are different.
    >
    > > So, instead of having 2 drivers split the
    > > functionality, can you forego registering smo8800 ACPI driver on
    > > your whitelisted boxes and instead instantiate full i2c client
    > > device with properly assigned both address and IRQ and let lis3lv02d
    > > handle it (providing both accelerometer data and /dev/freefall)?
    >
    > With Michał we already discussed about it, see emails. Basically you can
    > enable/disable kernel modules at compile time or blacklist at runtime
    > (or even chose what will be compiled into vmlinux and what as external
    > .ko module).

    This can be solved with a bit of Kconfig/IS_ENABLED() code.

    > Some distributions blacklist i2c-i801.ko module... And

    Any particular reason for that?

    > there can be also problem with initialization of i2c-i801 driver (fix is
    > in commit a7ae81952cda, but does not have to work at every time!). So
    > that move on whitelisted machines can potentially cause disappearance of
    > /dev/freefall and users will not have hdd protection which is currently
    > working.

    Well, I gave you 2 possible solutions (roll your own i2c read/write,
    forward them to i2c client) or have faith in your implementation and let
    lis3lv02d handle it.

    The 3rd one is to possibly add a flag to disable host notify to IRQ
    mapping for given client (if Wolfram/Jean OK with it).

    Oh, the 4th one: change the irq in lis3lv02d.h to be "int" and change
    the check in lis3lv02d.c to be "lis->irq <= 0" and instantiate your
    i2c_client with board_info->irq = -1.

    Pick whichever you prefer.

    By the way, what do you need accelerometer for on these devices? They
    don't appear to be tablets that could use one...

    Thanks.

    --
    Dmitry

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