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From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: arnd@arndb.de, smohanad@codeaurora.org, jhugo@codeaurora.org,
	kvalo@codeaurora.org, bjorn.andersson@linaro.org,
	hemantk@codeaurora.org, linux-arm-msm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI controllers
Date: Mon, 17 Feb 2020 17:23:08 +0530	[thread overview]
Message-ID: <20200217115308.GA12429@Mani-XPS-13-9360> (raw)
In-Reply-To: <20200217114515.GA154666@kroah.com>

On Mon, Feb 17, 2020 at 12:45:15PM +0100, Greg KH wrote:
> On Mon, Feb 17, 2020 at 10:57:43AM +0530, Manivannan Sadhasivam wrote:
> > Hi Greg,
> > 
> > On Thu, Feb 13, 2020 at 07:53:02AM -0800, Greg KH wrote:
> > > On Thu, Feb 13, 2020 at 09:18:09PM +0530, Manivannan Sadhasivam wrote:
> > > > 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.
> > > 
> > > How can you reuse anything?
> > > 
> > > > And this assumption has deep rooted in MHI bus design.
> > > 
> > > Maybe I do not understand what this is at all, but a device can only be
> > > on one "bus" at a time.  How is that being broken here?
> > > 
> > 
> > Let me share some insight on how it is being used:
> > 
> > The MHI bus sits on top of the actual physical bus like PCI-E and requires
> > the physical bus for doing activities like allocating I/O virtual address,
> > runtime PM etc... The part which gets tied to the PCI-E from MHI is called MHI
> > controller driver. This MHI controller driver is also the actual PCI-E driver
> > managing the device.
> > 
> > For instance, we have QCA6390 PCI-E WLAN device. For this device, there is a
> > ath11k PCI-E driver and the same driver also registers as a MHI controller and
> > acts as a MHI controller driver. This is where I referred to reusing the PCI-E
> > struct device. It's not that MHI bus itself is reusing the PCI-E struct device
> > but we need the PCI-E device pointer to do above mentioned IOVA, PM operations
> > in some places. One of the usage is below:
> > 
> > ```
> > void *buf = dma_alloc_coherent(mhi_cntrl->dev, size, dma_handle, gfp);
> > ```
> > 
> > There was some discussion about it here: https://lkml.org/lkml/2020/1/27/21
> > 
> > The MHI bus itself has the struct device and it is the child of the physical
> > bus (PCI-E in this case).
> > 
> > Now coming to your actual question of why using a custom "MHI" prefix for
> > dev_ APIs. I agree that if we use the struct device of MHI bus it is not at all
> > needed. The fact that we are using "mhi_cntrl->dev" (which points to PCI-E dev)
> > is what confusing and it can be avoided.
> 
> You should also rename "dev" there, as that is really a "pci device".
> So use the real pci device and name it as "parent_pci" or something like
> that, so we know just by looking at it as to what it really is.
> 
> Especially as traditionally "->dev" is the device structure for _this_
> device, not another one.
> 

Okay, sure. I'll rename it as "pdev" to indicate it as the parent device.

Thanks,
Mani

> thanks,
> 
> greg k-h

  reply	other threads:[~2020-02-17 11:53 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31 13:49 [PATCH v2 00/16] Add MHI bus support Manivannan Sadhasivam
2020-01-31 13:49 ` [PATCH v2 01/16] docs: Add documentation for MHI bus Manivannan Sadhasivam
2020-01-31 22:57   ` Jeffrey Hugo
2020-01-31 13:49 ` [PATCH v2 02/16] bus: mhi: core: Add support for registering MHI controllers Manivannan Sadhasivam
2020-02-06 16:56   ` Greg KH
2020-02-11 19:11     ` Manivannan Sadhasivam
2020-02-11 19:22       ` Greg KH
2020-02-13 15:22         ` Manivannan Sadhasivam
2020-02-06 16:57   ` Greg KH
2020-02-11 18:41     ` Manivannan Sadhasivam
2020-02-11 19:20       ` Greg KH
2020-02-13 15:20         ` Manivannan Sadhasivam
2020-02-13 15:34           ` Greg KH
2020-02-13 15:48             ` Manivannan Sadhasivam
2020-02-13 15:53               ` Greg KH
2020-02-14 16:41                 ` Jeffrey Hugo
2020-02-17  5:27                 ` Manivannan Sadhasivam
2020-02-17 11:45                   ` Greg KH
2020-02-17 11:53                     ` Manivannan Sadhasivam [this message]
2020-02-17 11:59                   ` Greg KH
2020-02-17 13:04                     ` Manivannan Sadhasivam
2020-02-17 14:15                       ` Greg KH
2020-02-17 16:04                         ` Arnd Bergmann
2020-02-17 16:32                           ` Greg KH
2020-02-17 17:50                             ` Manivannan Sadhasivam
2020-02-06 17:08   ` Jeffrey Hugo
2020-01-31 13:49 ` [PATCH v2 03/16] bus: mhi: core: Add support for registering MHI client drivers Manivannan Sadhasivam
2020-01-31 23:00   ` Jeffrey Hugo
2020-01-31 13:49 ` [PATCH v2 04/16] bus: mhi: core: Add support for creating and destroying MHI devices Manivannan Sadhasivam
2020-02-06 16:16   ` Jeffrey Hugo
2020-01-31 13:49 ` [PATCH v2 05/16] bus: mhi: core: Add support for ringing channel/event ring doorbells Manivannan Sadhasivam
2020-02-06 20:14   ` Jeffrey Hugo
2020-01-31 13:49 ` [PATCH v2 06/16] bus: mhi: core: Add support for PM state transitions Manivannan Sadhasivam
2020-02-06 20:15   ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 07/16] bus: mhi: core: Add support for basic PM operations Manivannan Sadhasivam
2020-02-06 20:15   ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 08/16] bus: mhi: core: Add support for downloading firmware over BHIe Manivannan Sadhasivam
2020-02-06 20:15   ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 09/16] bus: mhi: core: Add support for downloading RDDM image during panic Manivannan Sadhasivam
2020-02-06 16:41   ` Jeffrey Hugo
2020-02-06 20:17     ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 10/16] bus: mhi: core: Add support for processing events from client device Manivannan Sadhasivam
2020-02-06 20:16   ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 11/16] bus: mhi: core: Add support for data transfer Manivannan Sadhasivam
2020-02-06 20:16   ` Jeffrey Hugo
2020-02-17 16:13   ` Arnd Bergmann
2020-02-17 16:47     ` Manivannan Sadhasivam
2020-02-18  5:51       ` Manivannan Sadhasivam
2020-02-18 14:34         ` Arnd Bergmann
2020-01-31 13:50 ` [PATCH v2 12/16] bus: mhi: core: Add uevent support for module autoloading Manivannan Sadhasivam
2020-02-06 20:16   ` Jeffrey Hugo
2020-01-31 13:50 ` [PATCH v2 13/16] MAINTAINERS: Add entry for MHI bus Manivannan Sadhasivam
2020-02-03 10:16   ` Andy Shevchenko
2020-02-04  7:05     ` Manivannan Sadhasivam
2020-01-31 13:50 ` [PATCH v2 14/16] net: qrtr: Add MHI transport layer Manivannan Sadhasivam
2020-02-03 18:12   ` Jakub Kicinski
2020-02-04  8:19     ` Manivannan Sadhasivam
2020-02-07  0:14       ` Chris Lew
2020-02-11  3:50         ` Manivannan Sadhasivam
2020-02-12  1:01           ` Chris Lew
2020-01-31 13:50 ` [PATCH v2 15/16] net: qrtr: Do not depend on ARCH_QCOM Manivannan Sadhasivam
2020-01-31 13:50 ` [PATCH v2 16/16] soc: qcom: Do not depend on ARCH_QCOM for QMI helpers Manivannan Sadhasivam

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