Re: [PATCH v1 2/7] nvmem: rmem: add write and protect support

[Sascha Hauer <s.hauer@pengutronix.de>]

On Fri, May 30, 2025 at 01:41:01PM +0200, Oleksij Rempel wrote:
> Add reg_write and reg_protect operations to the rmem NVMEM driver.
> This makes rmem devices writable (they were previously read-only via the
> NVMEM interface due to lacking reg_write) and allows specific regions
> to be marked read-only.
> 
> The primary motivation is to improve testing of NVMEM consumer code that
> handles write protection, by enabling rmem to emulate such hardware,
> particularly in sandbox environments.

This is some quite complex code with lots of possibilities to introduce
bugs. nvmem devices are rather small and your motivation is debugging,
so I suggest to invest 1/8 of the nvmem device in memory and use a
bitmap instead of lists of ranges.

> +/**
> + * rmem_ranges_overlap - Check if two memory ranges overlap.
> + * @offset1: Starting offset of the first range.
> + * @len1:    Length of the first range.
> + * @offset2: Starting offset of the second range.
> + * @len2:    Length of the second range.
> + *
> + * Compares two memory ranges, defined by their starting offsets and
> + * lengths, to determine if they have any common region. Ranges with
> + * zero length are considered non-overlapping.
> + *
> + * The ranges are treated as inclusive, i.e., a range starting at @offset
> + * with length @len covers all bytes from @offset to @offset + @len - 1.
> + *
> + * Return: True if the ranges overlap, false otherwise.
> + */
> +static bool rmem_ranges_overlap(unsigned int offset1, size_t len1,
> +				unsigned int offset2, size_t len2)
> +{

We already have region_overlap_size() for this.

Sascha

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