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Subject: Re: [PATCH] ata: ahci-platform: add reset control support
To:     Kunihiko Hayashi <hayashi.kunihiko@socionext.com>,
        Thierry Reding <thierry.reding@gmail.com>
Cc:     Tejun Heo <tj@kernel.org>,
        Patrice Chotard <patrice.chotard@st.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, linux-ide@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mediatek@lists.infradead.org
References: <1521768653-11824-1-git-send-email-hayashi.kunihiko@socionext.com>
 <20180405095429.GA7506@ulmo> <20180405202347.2803.4A936039@socionext.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <b2426da6-598c-8ab1-7576-7ca4a151cc2a@redhat.com>
Date:   Thu, 5 Apr 2018 13:30:35 +0200
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Hi,

On 05-04-18 13:23, Kunihiko Hayashi wrote:
> Hi Thierry,
> 
> On Thu, 5 Apr 2018 11:54:29 +0200
> Thierry Reding <thierry.reding@gmail.com> 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().
>>
>>  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.
> 
> I assume that I use "generic-ahci" driver directly, and this driver has
> no way to handle resets, so I sent this patch.
> 
> However, also as far as I look, some hardware-specific drivers handle their
> own resets, and call ahci_platform_{enable,disable}_resources().
> Surely there are paths to call reset control twice in such drivers.
> 
> Identically, when the driver also handle their own clocks, they have same issue.
> 
>> Given how this is one of the more hardware-specific bits, perhaps a
>> better way to do this is to move reset handling into a Uniphier driver
>> much like Tegra, Mediatek and ST?
> 
> Since it's difficult to write the resets in general with ahci_platform, I can prepare
> hardware-specific driver for our SoCs >
>> That said, I don't see SATA support for any of the Socionext hardware
>> either in the DT bindings or drivers/ata, so perhaps it'd be best to
>> back this out again until we have something that's more well tested?
> 
> I'm about to use the generic driver, and prepare our phy driver and
> DT bindings for our SoCs, but not yet.

If the AHCI controller on your SoC works with the generic driver +
a phy-driver using the generic phy framework, then IMHO that is
preferred over adding yet another SoC specific AHCI driver. If the
only reason to do a SoC specific AHCI driver is the need for resets,
then IMHO we should add a flags parameter to ahci_platform_get_resources
which specifies which resource-types to get and have the existing
drivers call ahci_platform_get_resources() without the flag to also
get resets, where as the generic driver would get resets.

Thierry that should solve the problem, right ?

 > Then it's no problem that we can back this out.

Yes reverting it for now is probably best, but I would like to see
it get re-introduced while at the same time adding a flags parameter
to ahci_platform_get_resources() and make the reset handling conditional
on the flags. This IMHO is better then introducing another SoC driver.

Regards,

Hans