Re: [PATCH RFC v3 0/7] mfd: ls2kbmc: multiple fixes for this driver

On Fri, Jul 31, 2026 at 4:24=E2=80=AFPM Miao Wang <[email protected]=
m> wrote:
>
> Hi,
>
> > 2026=E5=B9=B47=E6=9C=8831=E6=97=A5 16:07=EF=BC=8CHuacai Chen <chenhuaca=
[email protected]> =E5=86=99=E9=81=93=EF=BC=9A
> >
> > On Fri, Jul 24, 2026 at 5:28=E2=80=AFPM Miao Wang <shankerwangmiao@gmai=
l.com> wrote:
> >>
> >> Hi,
> >>
> >>> 2026=E5=B9=B47=E6=9C=8824=E6=97=A5 16:55=EF=BC=8CHuacai Chen <chenhua=
[email protected]> =E5=86=99=E9=81=93=EF=BC=9A
> >>>
> >>> Hi, Miao,
> >>>
> >>> On Fri, Jul 10, 2026 at 1:24=E2=80=AFAM Miao Wang via B4 Relay
> >>> <[email protected]> wrote:
> >>>>
> >>>> Previously, the driver has been introduced to support the Loongson 2=
K
> >>>> BMC running on the Loongson Servers, which is essential to prevent
> >>>> the system from hanging when the BMC is being reset and the default
> >>>> efi-framebuffer is being used. However, there are some drawbacks in =
the
> >>>> driver.
> >>>>
> >>>> Firstly, the driver tries to read and write to the connected PCI-E h=
ost
> >>>> controller registers, assuming that the BMC is connected to LS7A PCI=
-E
> >>>> host controller. This assumption should be true for real products, b=
ut
> >>>> to prevent from accidentally reading and writing to the wrong PCI-E =
host
> >>>> controller, this driver should be modified to check this before
> >>>> accessing the registers.
> >>>>
> >>>> Secondly, the driver uses non-exported functions to tell the vt
> >>>> subsystem to redraw the screen, preventing the driver from being
> >>>> compiling as a module. This can be fixed by using the exported
> >>>> functions instead.
> >>> You can replace the redraw function, but I don't think it is necessar=
y
> >>> to make the bmc driver modular.
> >>>
> >>> BMC core, IPMI and simpledrm display are usually (if not always)
> >>> supposed to work as early as possible.
> >>
> >> I believe that it should be the user's decision to choose whether to
> >> compile a module into the kernel or as a module and it would be better
> >> if we can provide the possibilities for the user to choose from.
> >> Additionally, I don't think these modules are supposed to work that
> >> early. The mfd module provide two functions, the display and the ipmi
> >> device. In the aspect of graphical display, without this module, the
> >> user can still see the output during booting on their monitors, since
> >> efifb is working, providing a basic display function. In the aspect of
> >> the ipmi device, I don't think the lack of such device will influence
> >> the boot of the system, since it is a common practice to compile ipmi
> >> device drivers as modules on other architectures. As a result, neither
> >> of the two functions are required to be loaded that early and it is
> >> reasonable to at lease leave the choice to compile it as a module
> >> to the user.
> > Flexibility is not always useful, if a config doesn't provide good
> > effect, then it just increases complexity and makes maintenance more
> > difficult.
>
> I should emphasize that to allow this driver to be a module, there is
> no such increase on maintenance. Moreover, not all loongarch machines
> are requiring this driver. Especially only a part of the server models
> are quipped with this BMC. Comparing with other architectures, the
> driver for BMC are normally compiled as a module, such as mgag200 for
> iLO from HPE and iDRAC from DELL, hibmc_drm for Kunpeng server from
> Huawei. None of these BMC drivers requiring to be compiled into the
> kernel. I cannot see there is any reason keeping the driver from being
> allowed to be compiled as a module. I also do not think it will bring
> any significant maintenance burden. Implementing correct cleanup code
> should be necessary instead of burden.
Can we split into two series, one fix bugs and the others make bmc modular?

Otherwise I don't think we can reach a consensus in the near future.

Huacai

>
> Cheers,
>
> Miao Wang
>
>