linux-kernel - [PATCH 0/2] nvmem: imx-ocotp: allow reads with arbitrary size and offset

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Date:   Tue, 23 Jul 2019 17:32:41 +0200
From:   Jose Diaz de Grenu <Jose.DiazdeGrenu@...i.com>
To:     <Jose.DiazdeGrenu@...i.com>
CC:     <srinivas.kandagatla@...aro.org>, <shawnguo@...nel.org>,
        <s.hauer@...gutronix.de>, <kernel@...gutronix.de>,
        <festevam@...il.com>, <linux-imx@....com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 0/2] nvmem: imx-ocotp: allow reads with arbitrary size and offset

Currently the imx-ocotp driver does only allow reading complete OTP words
correcty aligned.

Usually OTP memory is limited, so the fields are stored using as few bits as
possible. This means that a given value rarely uses 32 bits and happens to be
aligned.

Even though the NVMEM API offers a way to define offset and size of each cell
(at bit level) this is not currently usable iwth the imx-ocotp driver, which
forces consumers to read complete words and then hardcode the necessary
shifting and masking in the driver code. 

As an example take the nvmem consumer imx_thermal.c, which reads nvmem cells
as uint32_t words:

	ret = nvmem_cell_read_u32(&pdev->dev, "calib", &val);
	if (ret)
		return ret;

	ret = imx_init_calib(pdev, val);
	if (ret)
		return ret;

	ret = nvmem_cell_read_u32(&pdev->dev, "temp_grade", &val);
	if (ret)
		return ret;
	imx_init_temp_grade(pdev, val);

but needs to later adjust the values in code:

	// Inside imx_init_calib()
	data->c1 = (ocotp_ana1 >> 9) & 0x1ff;

	// Inside imx_init_temp_grade()
	switch ((ocotp_mem0 >> 6) & 0x3) {

This patch adjusts the driver so that reads can be requested using any size
and offset. Then, for example the nvmem cell "calib" could use the 'bits'
property to specify size and offset in bits, removing the need to mask and
shift in the driver code.

This is specially useful when several drivers use the same nvmem cell and when
the specific size and offset of a OTP value depends on a hardware version.

Jose Diaz de Grenu (2):
  nvmem: imx-ocotp: use constant for write restriction
  nvmem: imx-ocotp: allow reads with arbitrary size and offset

 drivers/nvmem/imx-ocotp.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)