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

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Message-ID: <20230531150143.GI7968@thinkpad>
Date:   Wed, 31 May 2023 20:31:43 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Jeffrey Hugo <quic_jhugo@...cinc.com>, kuba@...nel.org,
        andersson@...nel.org, daniel@...ll.ch, mhi@...ts.linux.dev,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@...cinc.com>
Subject: Re: [PATCH] bus: mhi: host: Add userspace character interface

On Wed, May 31, 2023 at 03:35:08PM +0100, 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@codeaurora.org/
> > 
> > On Mon, May 22, 2023 at 01:04:59PM -0600, Jeffrey Hugo wrote:
> > > From: Pranjal Ramajor Asha Kanojiya <quic_pkanojiy@...cinc.com>
> > > 
> > > 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@...cinc.com>
> > > [jhugo: Rename to uci, plumb to mhi, rewrite commit text]
> > > Signed-off-by: Jeffrey Hugo <quic_jhugo@...cinc.com>
> > 
> > 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?
> 

Well, I was referring to the concept of UCI in general. Ofc, the build failure
need to be fixed.

- Mani

> confused,
> 
> greg k-h
> 

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