Re: [PATCH v2 00/21] ipmi: Allow raw access to KCS devices

[Andrew Jeffery]

On Thu, 8 Apr 2021, at 21:44, Corey Minyard wrote:
> On Thu, Apr 08, 2021 at 10:27:46AM +0930, Andrew Jeffery wrote:
> > Hi Corey,
> > 
> > On Fri, 19 Mar 2021, at 16:49, Andrew Jeffery wrote:
> > > Hello,
> > > 
> > > This series is a bit of a mix of things, but its primary purpose is to
> > > expose BMC KCS IPMI devices to userspace in a way that enables userspace
> > > to talk to host firmware using protocols that are not IPMI.
> > > 
> > > v1 can be found here:
> > > 
> > > https://lore.kernel.org/openbmc/20210219142523.3464540-1-andrew@xxxxxxxx/
> > > 
> > > Changes in v2 include:
> > > 
> > > * A rebase onto v5.12-rc2
> > > * Incorporation of off-list feedback on SerIRQ configuration from
> > >   Chiawei
> > > * Further validation on hardware for ASPEED KCS devices 2, 3 and 4
> > > * Lifting the existing single-open constraint of the IPMI chardev
> > > * Fixes addressing Rob's feedback on the conversion of the ASPEED KCS
> > >   binding to dt-schema
> > > * Fixes addressing Rob's feedback on the new aspeed,lpc-interrupts
> > >   property definition for the ASPEED KCS binding
> > > 
> > > A new chardev device is added whose implementation exposes the Input
> > > Data Register (IDR), Output Data Register (ODR) and Status Register
> > > (STR) via read() and write(), and implements poll() for event
> > > monitoring.
> > > 
> > > The existing /dev/ipmi-kcs* chardev interface exposes the KCS devices in
> > > a way which encoded the IPMI protocol in its behaviour. However, as
> > > LPC[0] KCS devices give us bi-directional interrupts between the host
> > > and a BMC with both a data and status byte, they are useful for purposes
> > > beyond IPMI.
> > > 
> > > As a concrete example, libmctp[1] implements a vendor-defined MCTP[2]
> > > binding using a combination of LPC Firmware cycles for bulk data
> > > transfer and a KCS device via LPC IO cycles for out-of-band protocol
> > > control messages[3]. This gives a throughput improvement over the
> > > standard KCS binding[4] while continuing to exploit the ease of setup of
> > > the LPC bus for early boot firmware on the host processor.
> > > 
> > > The series takes a bit of a winding path to achieve its aim:
> > > 
> > > 1. It begins with patches 1-5 put together by Chia-Wei, which I've
> > > rebased on v5.12-rc2. These fix the ASPEED LPC bindings and other
> > > non-KCS LPC-related ASPEED device drivers in a way that enables the
> > > SerIRQ patches at the end of the series. With Joel's review I'm hoping
> > > these 5 can go through the aspeed tree, and that the rest can go through
> > > the IPMI tree.
> > > 
> > > 2. Next, patches 6-13 fairly heavily refactor the KCS support in the
> > > IPMI part of the tree, re-architecting things such that it's possible to
> > > support multiple chardev implementations sitting on top of the ASPEED
> > > and Nuvoton device drivers. However, the KCS code didn't really have
> > > great separation of concerns as it stood, so even if we disregard the
> > > multiple-chardev support I think the cleanups are worthwhile.
> > > 
> > > 3. Patch 14 adds some interrupt management capabilities to the KCS
> > > device drivers in preparation for patch 16, which introduces the new
> > > "raw" KCS device interface. I'm not stoked about the device name/path,
> > > so if people are looking to bikeshed something then feel free to lay
> > > into that.
> > > 
> > > 4. The remaining patches switch the ASPEED KCS devicetree binding to
> > > dt-schema, add a new interrupt property to describe the SerIRQ behaviour
> > > of the device and finally clean up Serial IRQ support in the ASPEED KCS
> > > driver.
> > > 
> > > Rob: The dt-binding patches still come before the relevant driver
> > > changes, I tried to keep the two close together in the series, hence the
> > > bindings changes not being patches 1 and 2.
> > > 
> > > I've exercised the series under qemu with the rainier-bmc machine plus
> > > additional patches for KCS support[5]. I've also substituted this series in
> > > place of a hacky out-of-tree driver that we've been using for the
> > > libmctp stack and successfully booted the host processor under our
> > > internal full-platform simulation tools for a Rainier system.
> > > 
> > > Note that this work touches the Nuvoton driver as well as ASPEED's, but
> > > I don't have the capability to test those changes or the IPMI chardev
> > > path. Tested-by tags would be much appreciated if you can exercise one
> > > or both.
> > > 
> > > Please review!
> > 
> > Unfortunately the cover letter got detached from the rest of the series.
> > 
> > Any chance you can take a look at the patches?
> 
> There were some minor concerns that were unanswered, and there really
> was no review by others for many of the patches.

Right; I was planning to clean up the minor concerns once I'd received 
some more feedback. I could have done a better job of communicating 
that :)

> 
> I would like this patch set, it makes some good cleanups.  But I would
> like some more review and testing by others, if possible. 

No worries. I'm trying to rope some others in to take a look.

Thanks for the response.

Andrew