linux-kernel - Re: [PATCH 3/3] mmc: sdhci-of-arasan: Add support for ZynqMP Platform Tap Delays Setup

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Message-ID: <CAPDyKFp6O8rPZDZS4iKJam2+tXeen_ZMOXKw=WVzJNpBXcSc9g@mail.gmail.com>
Date:   Mon, 17 Jun 2019 16:58:47 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Manish Narani <manish.narani@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Adrian Hunter <adrian.hunter@...el.com>, rajan.vaja@...inx.com,
        jolly.shah@...inx.com, nava.manne@...inx.com,
        Olof Johansson <olof@...om.net>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] mmc: sdhci-of-arasan: Add support for ZynqMP Platform
 Tap Delays Setup

[...]

> >>
> >>
> >>> In regards to the mmc data part, I suggest to drop the
> >>> ->set_tap_delay() callback, but rather use a boolean flag to indicate
> >>> whether clock phases needs to be changed for the variant. Potentially
> >>> that could even be skipped and instead call clk_set_phase()
> >>> unconditionally, as the clock core deals fine with clock providers
> >>> that doesn't support the ->set_phase() callback.
> >>
> >> In connection to another version of this driver for latest Xilinx chip
> >> it would be better to keep set_tap_delay callback in the driver. The
> >> reason is that new chip/ip is capable to setup tap delays directly
> >> without asking firmware to do it. That's why for versal IP there is a
> >> need to call different setup_tap_delay function.
> >
> > The ->set_tap_delay() callback is for ZyncMp pointing to
> > sdhci_arasan_zynqmp_set_tap_delay(). This function calls the
> > clk_set_phase() API.
> >
> > What does ->set_tap_delay() do for the latest version?
>
> There is different set of default tap delays which should be programmed
> and it is done just via writing to registers which are the part of
> controller address space.

Okay, I see.

Not sure what makes most sense to do here, but it sounds to me like
another ->set_phase() callback should be implemented for the clock
provider. In other words, calling clk_set_phase() should continue to
works just fine for this case as well. If it turns out to be
inconvenient, we can always add the ->set_tap_delay() at a later point
when it makes more sense.

[...]

Kind regards
Uffe