Re: [PATCH v6 09/17] nvmem: microchip-otpc: nvmem: microchip-otpc: add tag-based packet lookup
Andy Shevchenko <[email protected]>
| Newsgroups | org.kernel.vger.linux-iio,org.infradead.lists.linux-arm-kernel,org.kernel.vger.linux-devicetree,org.kernel.vger.linux-kernel |
|---|---|
| Organization | Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs, Bertel Jungin Aukio 5, 02600 Espoo |
| Message-ID | <[email protected]> |
On Thu, Aug 06, 2026 at 01:10:16PM +0530, Varshini Rajendran wrote:
> Add support for accessing OTP packets by their tag which is a FourCC
> while preserving backward compatibility with the existing ID-based
> lookup.
>
> The OTP memory layout can vary across devices and may change over time,
> making the packet ID approach unreliable when the memory map is not
> known in advance. The packet tag provides a reliable way to identify
> and access packets without prior knowledge of the OTP memory layout.
>
> Two offset encodings are now supported:
> 1. Legacy ID-based: offset = OTP_PKT(id) = id * 4
> Used in DT as: reg = <OTP_PKT(1) 76>;
> 2. TAG-based: offset = 4-byte ASCII packet tag (FourCC)
> Used in DT as: reg = <0x41435354 0x4c>; (tag "ACST")
>
> The driver resolves offsets matching valid legacy selectors (multiples
> of 4 within the packet count) through ID lookup, falling back to tag
> lookup for other valid values. This ensures existing device trees
> continue to work while enabling new tag-based access. During probe,
> packet meta data including the tag is read and cached.
>
> The stride of the nvmem memory is set to 1 in order to support tag based
> offsets, comment in the header file is updated accordingly.
...
> +static bool mchp_otpc_is_valid_fourcc(u32 tag)
> +{
> + int i;
> + u8 c;
> +
> + for (i = 0; i < 4; i++) {
for (unsigned int i = 0; i < sizeof(tag); i++) {
> + c = (tag >> (i * 8)) & 0xff;
> + if (c < 0x20 || c > 0x7e)
> + return false;
> + }
> +
> + return true;
> +}
--
With Best Regards,
Andy Shevchenko