linux-kernel - Re: [PATCH] power: reset: msm: Add support for download-mode control

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Date:   Sun, 16 Sep 2018 13:28:50 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] power: reset: msm: Add support for download-mode control

Hi,

What's the status of this patch? It looks good to me, should it be
merged, did I miss a newer version?

-- Sebastian

On Fri, Jul 20, 2018 at 10:44:53AM -0700, Stephen Boyd wrote:
> Quoting Rajendra Nayak (2018-07-18 23:59:20)
> > 
> > 
> > On 7/19/2018 11:12 AM, Bjorn Andersson wrote:
> > > On Wed 18 Jul 22:18 PDT 2018, Rajendra Nayak wrote:
> > > 
> > >> commit '8c1b7dc9b: firmware: qcom: scm: Expose download-mode control'
> > >> added support for download-mode control using the scm firmware
> > >> driver for platforms which require a secure call to write the magic
> > >> cookie into the tcsr location.
> > >>
> > >> For platforms which *do not* need an scm call and where the kernel can
> > >> write the cookie by a direct read/write, add similar support in the
> > >> msm-poweroff driver.
> > >> Similar to the scm driver, the msm-poweroff driver clears the cookie
> > >> during a clean reboot.
> > >>
> > >> Download mode using msm-poweroff driver can be enabled by including
> > >> msm-poweroff.download_mode=1 on the command line.
> > >>
> > > 
> > > Should have thought about this when I wrote the scm code...
> > > 
> > > I would prefer if we could find a way to consolidate the two
> > > implementations behind the same Kconfig and command line parameters.
> > 
> > The only problem I saw with this was that *both* drivers would think
> > its enabled and try their own ways to enable it, and one of it would
> > always fail. We could fail silently, which would mean we will miss
> > cases when its a genuine failure but that should be fine?
> 
> Should be fine if SCM fails silently. If TCSR is specified it better
> work because that doesn't really rely on anything besides writing into a
> memory location.
> 
> > 
> > >> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
> > >> ---
> > >>   .../bindings/power/reset/msm-poweroff.txt          |  3 ++
> > >>   drivers/power/reset/Kconfig                        | 11 +++++++
> > >>   drivers/power/reset/msm-poweroff.c                 | 38 ++++++++++++++++++++++
> > >>   3 files changed, 52 insertions(+)
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/power/reset/msm-poweroff.txt b/Documentation/devicetree/bindings/power/reset/msm-poweroff.txt
> > >> index ce44ad3..9dd489f 100644
> > >> --- a/Documentation/devicetree/bindings/power/reset/msm-poweroff.txt
> > >> +++ b/Documentation/devicetree/bindings/power/reset/msm-poweroff.txt
> > >> @@ -8,6 +8,9 @@ settings.
> > >>   Required Properties:
> > >>   -compatible: "qcom,pshold"
> > >>   -reg: Specifies the physical address of the ps-hold register
> > >> +Optional Properties:
> > >> +-qcom,dload-mode: phandle to the TCSR hardware block and offset of the
> > >> +             download mode control register
> > >>   
> > >>   Example:
> > >>   
> > >> diff --git a/drivers/power/reset/Kconfig b/drivers/power/reset/Kconfig
> > >> index df58fc8..0c97e34 100644
> > >> --- a/drivers/power/reset/Kconfig
> > >> +++ b/drivers/power/reset/Kconfig
> > >> @@ -104,6 +104,17 @@ config POWER_RESET_MSM
> > >>      help
> > >>        Power off and restart support for Qualcomm boards.
> > >>   
> > >> +config POWER_RESET_MSM_DOWNLOAD_MODE
> > > 
> > > How about moving QCOM_SCM_DOWNLOAD_MODE_DEFAULT to
> > > drivers/soc/qcom/Kconfig (and removing "SCM") and referencing this in
> > > both drivers?
> > 
> > yes, thats possible, but I am not sure how to make the command line
> > option common for both. One other option I thought was if we could handle it
> > within the scm driver itself with an additional
> > binding to specify the non-secure download mode address.
> > something like qcom,dload-mode-ns?
> 
> Is the SCM device and driver always going to be present though? It may
> be better to make a TCSR platform device driver on designs that would
> configure the cookie with direct read/writes from Linux to break the
> relationship with scm entirely. Then the different configurations could
> flow from the DTS file either describing scm that has scm call, a
> special scm_writel address for TCSR, or a specific TCSR node with the
> address of the download mode cookie that triggers a TCSR driver to probe
> and register a reboot handler.
> 
> 

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