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

[Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>]

On 3/4/25 10:56 PM, Melody Olvera wrote:
> From: Wesley Cheng <quic_wcheng@quicinc.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@quicinc.com>
> Signed-off-by: Melody Olvera <quic_molvera@quicinc.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