linux-kernel - Re: [PATCH 01/16] docs: Add documentation for MHI bus

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Message-ID: <20200123133010.GB11366@mani>
Date:   Thu, 23 Jan 2020 19:00:10 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     gregkh <gregkh@...uxfoundation.org>, smohanad@...eaurora.org,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        hemantk@...eaurora.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH 01/16] docs: Add documentation for MHI bus

On Thu, Jan 23, 2020 at 02:19:51PM +0100, Arnd Bergmann wrote:
> On Thu, Jan 23, 2020 at 2:10 PM Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > On Thu, Jan 23, 2020 at 01:58:22PM +0100, Arnd Bergmann wrote:
> > > On Thu, Jan 23, 2020 at 12:18 PM Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org> wrote:
> > >
> > > I don't see any callers of mhi_register_controller(). Did I just miss it or did
> > > you not post one? I'm particularly interested in where the configuration comes
> > > from, is this hardcoded in the driver, or parsed from firmware or from registers
> > > in the hardware itself?
> > >
> >
> > I have not included the controller driver in this patchset. But you can take a
> > look at the ath11k controller driver here:
> > https://git.linaro.org/people/manivannan.sadhasivam/linux.git/tree/drivers/net/wireless/ath/ath11k/mhi.c?h=ath11k-qca6390-mhi#n13
> >
> > So the configuration comes from the static structures defined in the controller
> > driver. Earlier revision derived the configuration from devicetree but there are
> > many cases where this MHI bus is being used in non DT environments like x86.
> > So inorder to be platform agnostic, we chose static declaration method.
> >
> > In future we can add DT/ACPI support for the applicable parameters.
> 
> What determines the configuration? Is this always something that is fixed
> in hardware, or can some of the properties be changed based on what
> firmware runs the device?
> 

AFAIK, these configurations are fixed in hardware (this could come from
the firmware I'm not sure but they don't change with firmware revisions
for sure)

The reason for defining in the driver itself implies that these don't
change. But I'll confirm this with Qcom folks.

Thanks,
Mani

> If this is determined by the firmware, maybe the configuration would also
> need to be loaded from the file that contains the firmware, which in turn
> could be a blob in DT.
> 
>      Arnd