linux-kernel - RE: [PATCH 2/2] usb: dwc3: Add driver for Xilinx platforms

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Date:   Wed, 09 Sep 2020 13:26:42 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Manish Narani <MNARANI@...inx.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Michal Simek <michals@...inx.com>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git <git@...inx.com>
Subject: RE: [PATCH 2/2] usb: dwc3: Add driver for Xilinx platforms


Hi,

Manish Narani <MNARANI@...inx.com> writes:
>> -----Original Message-----
>> From: Felipe Balbi <balbi@...nel.org>
>> Sent: Tuesday, September 1, 2020 5:45 PM
>> 
>> >> > +		goto err;
>> >> > +	}
>> >> > +
>> >> > +	ret = dwc3_xlnx_rst_assert(priv_data->apbrst);
>> >> > +	if (ret < 0) {
>> >> > +		dev_err(dev, "%s: %d: Failed to assert reset\n",
>> >> > +			__func__, __LINE__);
>> >>
>> >> 		dev_err(dev, "Failed to assert APB reset\n");
>> >>
>> >> > +		goto err;
>> >> > +	}
>> >> > +
>> >> > +	ret = phy_init(priv_data->usb3_phy);
>> >>
>> >> dwc3 core should be handling this already
>> >
>> > The USB controller used in Xilinx ZynqMP platform uses xilinx GT phy
>> > which has 4 GT lanes and can used by 4 peripherals at a time.
>> 
>> At the same time or are they mutually exclusive?
>
> The lanes are mutually exclusive.

Thank you for confirming :-)

>  [...]
>> >> > +	if (ret < 0) {
>> >> > +		dev_err(dev, "%s: %d: Failed to release reset\n",
>> >> > +			__func__, __LINE__);
>> >> > +		goto err;
>> >> > +	}
>> >> > +
>> >> > +	/* Set PIPE power present signal */
>> >> > +	writel(PIPE_POWER_ON, priv_data->regs + PIPE_POWER_OFFSET);
>> >> > +
>> >> > +	/* Clear PIPE CLK signal */
>> >> > +	writel(PIPE_CLK_OFF, priv_data->regs + PIPE_CLK_OFFSET);
>> >>
>> >> shouldn't this be hidden under clk_enable()?
>> >
>> > Though its naming suggests something related to clock framework, it is
>> > a register in the Xilinx USB controller space which configures the
>> > PIPE clock coming from Serdes.
>> 
>> PIPE clock is a clock. It just so happens that the source is the PHY
>> itself.
>
> This bit is used to choose between PIPE clock coming from SerDes
> and the Suspend Clock. When the controller is out of reset, this bit
> needs to be reset in order to make the USB controller work. This
> register is added in Xilinx USB controller register space. I will
> add more description about the same in v2.

Aha! That clarifies. It's just a clock selection from clocks that are
generated elsewhere :-) I guess a clk driver would be overkill, indeed.

Thanks for explaining. Could you add some of this information to commit
log, then?

cheers

-- 
balbi

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