linux-kernel - Re: [PATCH v2 6/9] phy: qcom: Add M31 based eUSB2 PHY driver

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Message-ID: <69fa7f33-e957-4dac-93dc-6fd40167873c@oss.qualcomm.com>
Date: Tue, 11 Mar 2025 12:19:01 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Melody Olvera <quic_molvera@...cinc.com>, Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 6/9] phy: qcom: Add M31 based eUSB2 PHY driver

On 3/4/25 10:56 PM, Melody Olvera wrote:
> From: Wesley Cheng <quic_wcheng@...cinc.com>
> 
> SM8750 utilizes an eUSB2 PHY from M31.  Add the initialization
> sequences to bring it out of reset and into an operational state.  This
> differs to the M31 USB driver, in that the M31 eUSB2 driver will
> require a connection to an eUSB2 repeater.  This PHY driver will handle
> the initialization of the associated eUSB2 repeater when required.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> Signed-off-by: Melody Olvera <quic_molvera@...cinc.com>
> ---

[...]

> +static int msm_m31_eusb2_write_readback(void __iomem *base, u32 offset,
> +					const u32 mask, u32 val)
> +{
> +	u32 write_val;
> +	u32 tmp;
> +
> +	tmp = readl_relaxed(base + offset);
> +	tmp &= ~mask;
> +	write_val = tmp | val;
> +
> +	writel_relaxed(write_val, base + offset);
> +
> +	tmp = readl_relaxed(base + offset);
> +	tmp &= mask;
> +
> +	if (tmp != val) {
> +		pr_err("write: %x to offset: %x FAILED\n", val, offset);
> +		return -EINVAL;
> +	}
> +
> +	return 0;

Is there a reason we need to read back every write?

Does this have to do with some funny write buffering?

Konrad