Re: [PATCH v4 0/3] LoongArch: Add Loongson-2K BMC support

[Corey Minyard]

On Sat, Jun 14, 2025 at 10:50:37AM +0800, Binbin Zhou wrote:
> Hi Corey:
> 
> On Sat, Jun 14, 2025 at 8:41 AM Corey Minyard <corey@xxxxxxxxxxx> wrote:
> >
> > On Fri, Jun 13, 2025 at 02:43:38PM +0800, Binbin Zhou wrote:
> > > Hi all:
> > >
> > > This patch set introduces the Loongson-2K BMC.
> > >
> > > It is a PCIe device present on servers similar to the Loongson-3 CPUs.
> > > And it is a multifunctional device (MFD), such as display as a sub-function
> > > of it.
> >
> > I've asked this before, but I haven't gotten a answer, I don't think.
> >
> > Is this really a multi-function device?  Is there (or will there be)
> > another driver that uses the MFD code?
> 
> I am very sorry, I may have overlooked your previous question.
> 
> And I also may not have a thorough understanding of multifunction devices.
> 
> The Loongson-2K BMC device provides two functions: display and IPMI.
> For display, we pass the simplefb_platform_data parameter and register
> the simpledrm device, as shown in patch-1.
> 
> Therefore, I think this should be considered a multifunction device.

Ok, that's clear, thank you.

However, that's not really very clear from the patches you have
provided.  Particularly, the "bmc" in the name from patch 1 makes one
think that it's only a bmc.

The "bmc" name is also a little confusing; the devices with a "bmc" in
the name are all the BMC side, but you are doing a host side device.

If you look at most of the other MFDs, they have a "core" section then
various other parts that use the core.  And possibly parts in other
directories for individual functions.  I think you need to do the same
design.  Have a "core" section that both the display and bmc use, then a
separate display and bmc driver.

That way, you can use the display without the IPMI interface, or the
IPMI interface without the display.

I would like to see:

* A core mfd device named ls2k-core.c that has the core functions.
  It would have its own config item (MFD_LS2K) that would be
  selected if either the display or IPMI device is enabled.

* A separate display device in its own file with its own config item.
  This isn't my area, so I'm not sure where this should go.

* The IPMI device in the ipmi directory named ipmi_ls2k.c, again
  with it's own config item (IPMI_LS2K).

Does that make sense?  I don't want to make things too hard, but that's
the way pretty much everything else is done on MFDs.

Thanks,

-corey

> 
> >
> > If nothing else is going to use this, then it's really not a
> > multi-function device and all the code can go into the IPMI directory.
> > That simplifies maintenance.
> >
> > If it is a multi-function device, then I want two separate Kconfig
> > items, one for the MFD and one for the IPMI portion.  That way it's
> > ready and you don't have to bother about the IPMI portion when
> > adding the other device.
> >
> > All else looks good, I think.
> >
> > -corey
> >
> > >
> > > For IPMI, according to the existing design, we use software simulation to
> > > implement the KCS interface registers: Stauts/Command/Data_Out/Data_In.
> > >
> > > Also since both host side and BMC side read and write kcs status, we use
> > > fifo pointer to ensure data consistency.
> > >
> > > For the display, based on simpledrm, the resolution is read from a fixed
> > > position in the BMC since the hardware does not support auto-detection
> > > of the resolution. Of course, we will try to support multiple
> > > resolutions later, through a vbios-like approach.
> > >
> > > Especially, for the BMC reset function, since the display will be
> > > disconnected when BMC reset, we made a special treatment of re-push.
> > >
> > > Based on this, I will present it in four patches:
> > > patch-1: BMC device PCI resource allocation.
> > > patch-2: BMC reset function support
> > > patch-3: IPMI implementation
> > >
> > > Thanks.
> > >
> > > -------
> > > V4:
> > > - Add Reviewed-by tag;
> > > - Change the order of the patches.
> > > Patch (1/3):
> > >   - Fix build warning by lkp: Kconfig tristate -> bool
> > >     - https://lore.kernel.org/all/202505312022.QmFmGE1F-lkp@xxxxxxxxx/
> > >  - Update commit message;
> > >  - Move MFD_LS2K_BMC after MFD_INTEL_M10_BMC_PMCI in Kconfig and
> > >    Makefile.
> > > Patch (2/3):
> > >   - Remove unnecessary newlines;
> > >   - Rename ls2k_bmc_check_pcie_connected() to
> > >     ls2k_bmc_pcie_is_connected();
> > >   - Update comment message.
> > > Patch (3/3):
> > >   - Remove unnecessary newlines.
> > >
> > > Link to V3:
> > > https://lore.kernel.org/all/cover.1748505446.git.zhoubinbin@xxxxxxxxxxx/
> > >
> > > V3:
> > > Patch (1/3):
> > >  - Drop "MFD" in title and comment;
> > >  - Fromatting code;
> > >  - Add clearer comments.
> > > Patch (2/3):
> > >  - Rebase linux-ipmi/next tree;
> > >  - Use readx()/writex() to read and write IPMI data instead of structure
> > >    pointer references;
> > >  - CONFIG_LOONGARCH -> MFD_LS2K_BMC;
> > >  - Drop unused output.
> > > Patch (3/3):
> > >  - Inline the ls2k_bmc_gpio_reset_handler() function to ls2k_bmc_pdata_initial();
> > >  - Add clearer comments.
> > >  - Use proper multi-line commentary as per the Coding Style documentation;
> > >  - Define all magic numbers.
> > >
> > > Link to V2:
> > > https://lore.kernel.org/all/cover.1747276047.git.zhoubinbin@xxxxxxxxxxx/
> > >
> > > V2:
> > > - Drop ls2kdrm, use simpledrm instead.
> > > Patch (1/3):
> > >  - Use DEFINE_RES_MEM_NAMED/MFD_CELL_RES simplified code;
> > >  - Add resolution fetching due to replacing the original display
> > >    solution with simpledrm;
> > >  - Add aperture_remove_conflicting_devices() to avoid efifb
> > >    conflict with simpledrm.
> > > Patch (3/3):
> > >  - This part of the function, moved from the original ls2kdrm to mfd;
> > >  - Use set_console to implement the Re-push display function.
> > >
> > > Link to V1:
> > > https://lore.kernel.org/all/cover.1735550269.git.zhoubinbin@xxxxxxxxxxx/
> > >
> > > Binbin Zhou (3):
> > >   mfd: ls2kbmc: Introduce Loongson-2K BMC core driver
> > >   mfd: ls2kbmc: Add Loongson-2K BMC reset function support
> > >   ipmi: Add Loongson-2K BMC support
> > >
> > >  drivers/char/ipmi/Makefile       |   1 +
> > >  drivers/char/ipmi/ipmi_si.h      |   7 +
> > >  drivers/char/ipmi/ipmi_si_intf.c |   3 +
> > >  drivers/char/ipmi/ipmi_si_ls2k.c | 189 ++++++++++++
> > >  drivers/mfd/Kconfig              |  12 +
> > >  drivers/mfd/Makefile             |   2 +
> > >  drivers/mfd/ls2kbmc-mfd.c        | 485 +++++++++++++++++++++++++++++++
> > >  7 files changed, 699 insertions(+)
> > >  create mode 100644 drivers/char/ipmi/ipmi_si_ls2k.c
> > >  create mode 100644 drivers/mfd/ls2kbmc-mfd.c
> > >
> > >
> > > base-commit: cd2e103d57e5615f9bb027d772f93b9efd567224
> > > --
> > > 2.47.1
> > >
> 
> 
> -- 
> Thanks.
> Binbin