linux-kernel - Re: [PATCH v4 3/6] nvmem: sec-qfprom: Add Qualcomm secure QFPROM support.

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Message-ID: <20230630200325.GA1059662@hu-bjorande-lv.qualcomm.com>
Date:   Fri, 30 Jun 2023 13:03:25 -0700
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
CC:     Komal Bajaj <quic_kbajaj@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] nvmem: sec-qfprom: Add Qualcomm secure QFPROM
 support.

On Fri, Jun 23, 2023 at 04:53:44PM +0200, Konrad Dybcio wrote:
> On 23.06.2023 16:18, Komal Bajaj wrote:
> > diff --git a/drivers/nvmem/sec-qfprom.c b/drivers/nvmem/sec-qfprom.c
[..]
> > +static int sec_qfprom_reg_read(void *context, unsigned int reg, void *_val, size_t bytes)
> > +{
> > +	struct sec_qfprom_priv *priv = context;
> > +	u8 *val = _val;
> > +	u8 *tmp;
> > +	u32 read_val;
> > +	unsigned int i;
> Please sort this to look like a reverse-Christmas-tree
> 
> 
> > +
> > +	for (i = 0; i < bytes; i++, reg++) {
> > +		if (i == 0 || reg % 4 == 0) {
> > +			if (qcom_scm_io_readl(priv->qfpseccorrected + (reg & ~3), &read_val)) {
> > +				dev_err(priv->dev, "Couldn't access fuse register\n");
> > +				return -EINVAL;
> > +			}
> > +			tmp = (u8 *)&read_val;
> > +		}
> I don't understand this read-4-times dance.. qcom_scm_io_readl() reads
> u32, so this should be as simple as:
> 
> val[i + 0] = FIELD_GET(GENMASK(7, 0), reg);
> val[i + 1] = ..
> val[i + 2] = ..
> val[i + 3] = ..
> 

No need for FIELD_GET() to do that, you can just do *(u32*)val =
read_val; although this comes with alignment issues.


But, that this the length of val is always divisible by 4, and I
wasn't able to convince myself that it was the case...

So this is, pretty much, what I proposed in v3:
https://lore.kernel.org/linux-arm-msm/20230527205031.iwsujvlbxazukwfy@ripper/

Regards,
Bjorn

> 
> > +
> > +		val[i] = tmp[reg & 3];
> > +	}
> > +
> > +	return 0;