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Date:   Fri, 06 Apr 2018 13:48:39 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
To:     Hans de Goede <hdegoede@redhat.com>
Subject: Re: [PATCH] ata: ahci-platform: add reset control support
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Patrice CHOTARD <patrice.chotard@st.com>,
        Tejun Heo <tj@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        "linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mediatek@lists.infradead.org" 
        <linux-mediatek@lists.infradead.org>
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Hi Hans,

On Thu, 5 Apr 2018 16:08:24 +0200
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 05-04-18 16:00, Hans de Goede wrote:
> > Hi,
> > > On 05-04-18 15:54, Thierry Reding wrote:
> >> On Thu, Apr 05, 2018 at 03:27:03PM +0200, Hans de Goede wrote:
> >>> Hi,
> >>>
> >>> On 05-04-18 15:17, Patrice CHOTARD wrote:
> >>>> Hi Thierry
> >>>>
> >>>> On 04/05/2018 11:54 AM, Thierry Reding wrote:
> >>>>> On Fri, Mar 23, 2018 at 10:30:53AM +0900, Kunihiko Hayashi wrote:
> >>>>>> Add support to get and control a list of resets for the device
> >>>>>> as optional and shared. These resets must be kept de-asserted until
> >>>>>> the device is enabled.
> >>>>>>
> >>>>>> This is specified as shared because some SoCs like UniPhier series
> >>>>>> have common reset controls with all ahci controller instances.
> >>>>>>
> >>>>>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
> >>>>>> ---
> >>>>>> ??? .../devicetree/bindings/ata/ahci-platform.txt????? |? 1 +
> >>>>>> ??? drivers/ata/ahci.h???????????????????????????????? |? 1 +
> >>>>>> ??? drivers/ata/libahci_platform.c???????????????????? | 24 +++++++++++++++++++---
> >>>>>> ??? 3 files changed, 23 insertions(+), 3 deletions(-)
> >>>>>
> >>>>> This causes a regression on Tegra because we explicitly request the
> >>>>> resets after the call to ahci_platform_get_resources().
> >>>>
> >>>> I confirm, we got exactly the same behavior on STi platform.
> >>>>
> >>>>>
> >>>>> ?? From a quick look, ahci_mtk and ahci_st are in the same boat, adding the
> >>>>> corresponding maintainers to Cc.
> >>>>>
> >>>>> Patrice, Matthias: does SATA still work for you after this patch? This
> >>>>> has been in linux-next since next-20180327.
> >>>>
> >>>> SATA is still working after this patch, but a kernel warning is
> >>>> triggered due to the fact that resets are both requested by
> >>>> libahci_platform and by ahci_st driver.
> >>>
> >>> So in your case you might be able to remove the reset handling
> >>> from the ahci_st driver and rely on the new libahci_platform
> >>> handling instead? If that works that seems like a win to me.
> >>>
> >>> As said elsewhere in this thread I think it makes sense to keep (or re-add
> >>> after a revert) the libahci_platform reset code, but make it conditional
> >>> on a flag passed to ahci_platform_get_resources(). This way we get
> >>> the shared code for most cases and platforms which need special handling
> >>> can opt-out.
> >>
> >> Agreed, although I prefer such helpers to be opt-in, rather than
> >> opt-out. In my experience that tends make the helpers more resilient to
> >> this kind of regression. It also simplifies things because instead of
> >> drivers saying "I want all the helpers except this one and that one",
> >> they can simply say "I want these helpers and that one". In the former
> >> case whenever you add some new (opt-out) feature, you have to update all
> >> drivers and add the exception. In the latter you only need to extend the
> >> drivers that want to make use of the new helper.
> 
> Erm, the idea never was to make this opt-out but rather opt in, so
> we add a flags parameter to ahci_platform_get_resources() and all
> current users pass in 0 for that to keep the current behavior.
> 
> And only the generic drivers/ata/ahci_platform.c driver will pass
> in a the new AHCI_PLATFORM_GET_RESETS flag, which makes
> ahci_platform_get_resources() (and the other functions) also deal
> with resets.
> 
> >> With that in mind, rather than adding a flag to the
> >> ahci_platform_get_resources() function, it might be more flexible to
> >> split the helpers into finer-grained functions. That way drivers can
> >> pick whatever functionality they want from the helpers.
> > > Good point, so lets:
> > > 1) Revert the patch for now
> > 2) Have a new version of the patch which adds a ahci_platform_get_resets() helper
> > 3) Modify the generic drivers/ata/ahci_platform.c driver to call the new
> >  ?? ahci_platform_get_resets() between its ahci_platform_get_resources()
> >  ?? and ahci_platform_enable_resources() calls.
> >  ?? I think that ahci_platform_enable_resources() should still automatically
> >  ?? do the right thing wrt resets if ahci_platform_get_resets() was called
> >  ?? (otherwise the resets array will be empty and should be skipped)
> > > This should make the generic driver usable for the UniPhier SoCs and
> > maybe some other drivers like the ahci_st driver can also switch to the
> > new ahci_platform_get_resets() functionality to reduce their code a bit.
> 
> So thinking slightly longer about this, with the opt-in variant
> (which is what I intended all along) I do think that a flags parameter
> is better, because the whole idea behind lib_ahci_platform is to avoid
> having to do err = get_resource_a(), if (err) bail, err = get_resource_b()
> if (err) bail, etc. in all the ahci (platform) drivers. And having fine
> grained helpers re-introduces that.

In case of adding a flag instead of get_resource_a(),
for example, we add the flag for use of resets,

-struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev)
+struct ahci_host_priv *ahci_platform_get_resources(struct platform_device *pdev,
+                                                  bool use_reset)

and for now all the drivers using this function need to add the argument as false
to the caller.

-       hpriv = ahci_platform_get_resources(pdev);
+       hpriv = ahci_platform_get_resources(pdev, false);

Surely this can avoid adding functions such get_resource_a(). If we apply another
feature later, we add its flag as one of the arguments instead. Is it right?

Thank you,

---
Best Regards,
Kunihiko Hayashi