linux-kernel - Re: [PATCH 16/24] rtc: pm8xxx: add support for nvmem offset

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Date:   Fri, 27 Jan 2023 14:13:21 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Johan Hovold <johan+linaro@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/24] rtc: pm8xxx: add support for nvmem offset



On 26/01/2023 14:20, Johan Hovold wrote:
> On many Qualcomm platforms the PMIC RTC control and time registers are
> read-only so that the RTC time can not be updated. Instead an offset
> needs be stored in some machine-specific non-volatile memory, which the
> driver can take into account.
> 
> Add support for storing a 32-bit offset from the Epoch in an nvmem cell
> so that the RTC time can be set on such platforms.
> 
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
> ---
>   drivers/rtc/rtc-pm8xxx.c | 134 +++++++++++++++++++++++++++++++++++----
>   1 file changed, 123 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-pm8xxx.c b/drivers/rtc/rtc-pm8xxx.c
> index 922aef0f0241..09816b9f6282 100644
> --- a/drivers/rtc/rtc-pm8xxx.c
> +++ b/drivers/rtc/rtc-pm8xxx.c
> @@ -3,6 +3,7 @@
>    */
> +static int pm8xxx_rtc_read_nvmem_offset(struct pm8xxx_rtc *rtc_dd)
> +{
> +	size_t len;
> +	void *buf;
> +	int rc;
> +
> +	buf = nvmem_cell_read(rtc_dd->nvmem_cell, &len);
> +	if (IS_ERR(buf)) {
> +		rc = PTR_ERR(buf);
> +		dev_err(rtc_dd->dev, "failed to read nvmem offset: %d\n", rc);
> +		return rc;
> +	}
> +
> +	if (len != sizeof(u32)) {
> +		dev_err(rtc_dd->dev, "unexpected nvmem cell size %zu\n", len);
> +		kfree(buf);
> +		return -EINVAL;
> +	}
how about us nvmem_cell_read_u32()

> +
> +	rtc_dd->offset = get_unaligned_le32(buf);
> +
> +	kfree(buf);
> +
> +	return 0;
> +}
> +