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. I'll change it in next iteration. Thanks, Mani > thanks, > > greg k-h
