linux-kernel - Re: [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI controllers

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Date:   Thu, 13 Feb 2020 21:18:09 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, smohanad@...eaurora.org, jhugo@...eaurora.org,
        kvalo@...eaurora.org, bjorn.andersson@...aro.org,
        hemantk@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI
 controllers

Hi Greg,

On Thu, Feb 13, 2020 at 07:34:18AM -0800, Greg KH wrote:
> On Thu, Feb 13, 2020 at 08:50:13PM +0530, Manivannan Sadhasivam wrote:
> > On Tue, Feb 11, 2020 at 11:20:55AM -0800, Greg KH wrote:
> > > On Wed, Feb 12, 2020 at 12:11:30AM +0530, Manivannan Sadhasivam wrote:
> > > > Hi Greg,
> > > > 
> > > > On Thu, Feb 06, 2020 at 05:57:55PM +0100, Greg KH wrote:
> > > > > On Fri, Jan 31, 2020 at 07:19:55PM +0530, Manivannan Sadhasivam wrote:
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/bus/mhi/core/init.c
> > > > > > @@ -0,0 +1,407 @@
> > > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > > +/*
> > > > > > + * Copyright (c) 2018-2020, The Linux Foundation. All rights reserved.
> > > > > > + *
> > > > > > + */
> > > > > > +
> > > > > > +#define dev_fmt(fmt) "MHI: " fmt
> > > > > 
> > > > > This should not be needed, right?  The bus/device name should give you
> > > > > all you need here from what I can tell.  So why is this needed?
> > > > > 
> > > > 
> > > > The log will have only the device name as like PCI-E. But that won't specify
> > > > where the error is coming from. Having "MHI" prefix helps the users to
> > > > quickly identify that the error is coming from MHI stack.
> > > 
> > > If the driver binds properly to the device, the name of the driver will
> > > be there in the message, so I suggest using that please.
> > > 
> > > No need for this prefix...
> > > 
> > 
> > So the driver name will be in the log but that won't help identifying where
> > the log is coming from. This is more important for MHI since it reuses the
> > `struct device` of the transport device like PCI-E. For instance, below is
> > the log without MHI prefix:
> > 
> > [   47.355582] ath11k_pci 0000:01:00.0: Requested to power on
> > [   47.355724] ath11k_pci 0000:01:00.0: Power on setup success
> > 
> > As you can see, this gives the assumption that the log is coming from the
> > ath11k_pci driver. But the reality is, it is coming from MHI bus.
> 
> Then you should NOT be trying to "reuse" a struct device.
> 
> > With the prefix added, we will get below:
> > 
> > [   47.355582] ath11k_pci 0000:01:00.0: MHI: Requested to power on
> > [   47.355724] ath11k_pci 0000:01:00.0: MHI: Power on setup success
> > 
> > IMO, the prefix will give users a clear idea of logs and that will be very
> > useful for debugging.
> > 
> > Hope this clarifies.
> 
> Don't try to reuse struct devices, if you are a bus, have your own
> devices as that's the correct way to do things.
> 

I assumed that the buses relying on a different physical interface for the
actual communication can reuse the `struct device`. I can see that the MOXTET
bus driver already doing it. It reuses the `struct device` of SPI.

And this assumption has deep rooted in MHI bus design.

Thanks,
Mani

> thanks,
> 
> greg k-h