Re: [PATCH] bus: mhi: host: Add userspace character interface

[Jeffrey Hugo]

On 5/31/2023 9:04 AM, Jeffrey Hugo wrote:
> On 5/31/2023 8:35 AM, Greg KH wrote:
> > On Wed, May 31, 2023 at 07:58:03PM +0530, Manivannan Sadhasivam wrote:
> > > + Jakub (who NACKed the previous submission of UCI driver)
> > > Link to previous submission: 
> > > https://lore.kernel.org/all/1606533966-22821-1-git-send-email-hemantk@xxxxxxxxxxxxxx/ 
> > >
> > >
> > > On Mon, May 22, 2023 at 01:04:59PM -0600, Jeffrey Hugo wrote:
> > > > From: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@xxxxxxxxxxx>
> > > >
> > > > I2C, USB, and PCIe are examples of buses which have a mechanism to give
> > > > userspace direct access to a device on those buses. The MHI userspace
> > > > character interface (uci) is the MHI bus analogue.
> > > >
> > > > The MHI bus devices are MHI channels which ferry blocks of data from 
> > > > one
> > > > end to the other. With this simple purpose, we can define a simple
> > > > interface to userspace - a character device that supports 
> > > > open/close/read/
> > > > write/poll operations. Since bus devices can only have a single 
> > > > consumer
> > > > we encode a whitelist of MHI channels to be exported to userspace so as
> > > > to avoid conflicts.
> > > >
> > > > We also make this mechanism open to any device that implements MHI.
> > > > Today this includes WLAN (Wi-Fi), WWAN (4G/5G cellular), and ML/AI
> > > > devices. More devices are expected in the future.
> > > >
> > > > In addition to implementing the framework for uci, we include an 
> > > > initial
> > > > usecase - the QAIC Sahara device.
> > > >
> > > > Sahara is a file transfer protocol that is commonly used for two 
> > > > purposes
> > > > when interacting with a device - transferring firmware to the device 
> > > > and
> > > > transferring crashdumps from the device. The Sahara protocol puts the
> > > > receiver of the data in control of the transfer. A firmware transfer
> > > > operation would have the device requesting the specific firmware images
> > > > that the device wants, and the host satisfying those requests.
> > > >
> > > > In most cases, including for AIC100, Sahara is used as part of a two 
> > > > stage
> > > > loading process. The device will boot a very limited bootloader that 
> > > > does
> > > > the base minimum initialization and jump to the next stage. A 
> > > > simple, one-
> > > > shot protocol like BHI is used to send the next stage bootloader to the
> > > > device. This second stage bootloader contains more functionality and
> > > > implements the Sahara protocol. The second stage determines from 
> > > > various
> > > > inputs what set of runtime firmware is required to boot the device 
> > > > into an
> > > > operational status, and requests those pieces from the host.  With 
> > > > those
> > > > images transferred over, the device can funnly initialize.
> > > >
> > > > Each AIC100 instance (currently, up to 16) in a system will create a
> > > > MHI device for QAIC_SAHARA. MHI_uci will consume each of these and 
> > > > create
> > > > a unique chardev which will be found as
> > > > /dev/<mhi instance>_QAIC_SAHARA
> > > > For example - /dev/mhi0_QAIC_SAHARA
> > > >
> > > > An open userspace application that can consume these devices for 
> > > > firmware
> > > > transfers is located at https://github.com/andersson/qdl
> > > >
> > > > Signed-off-by: Pranjal Ramajor Asha Kanojiya 
> > > > <quic_pkanojiy@xxxxxxxxxxx>
> > > > [jhugo: Rename to uci, plumb to mhi, rewrite commit text]
> > > > Signed-off-by: Jeffrey Hugo <quic_jhugo@xxxxxxxxxxx>
> > >
> > > The previous attempt on adding UCI driver was NACKed by Jakub. For 
> > > merging this
> > > patch, I need an ACK from Jakub.
> >
> > Given that this fails the kernel robot tests, why would anyone ack it
> > as-is?
>
> I think Mani I looking for some "guidance" on the "architecture", and 
> frankly so am I.  An official Ack from Jakub might not be quite the 
> right thing at this stage, but at-least Jakub could come in and say he 
> isn't planning on NACKing this right off the bat, in particular because 
> this functionality can be used by WWAN devices which seems to be what 
> caused the mess the last time around.
>
> We've gone full circle here.  This functionality was proposed as part of 
> the bus.  Jakub came in an NACKed that, which resulted in the WWAN 
> subsystem and the guidance that this functionally belongs with the 
> devices.  I tried to put it with the AIC100/QAIC device based on that, 
> and that got NACKed by Daniel (GPU) saying that this belongs with the 
> bus.  You (Greg) seemed to agree with Daniel on that.
>
> Fixing kernel robot tests is one thing (I haven't seen any reports on 
> this iteration), but if there is no agreement on where this lives, isn't 
> it DOA?

I went hunting for a report and found it.  Not sure why it hasn't hit my 
inbox.  The issue looks trivial and really doesn't seem to prevent 
discussions on this IMO.

> In summary, if you don't like this, please give some clear guidance. 
> Greg, you've told me in the past that you don't discuss "architecture" 
> without seeing the code.  Here is some code.  I don't claim it is 
> perfect (you mentioned the QAIC version had some issues you were going 
> to help with), but I would like to see some input.
>
> -Jeff