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h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=i48MIGwzBxi2do2WYXSYPbruC3HoFCZMxRU1UUDDuYs=; b=I39l4qPTZiayixscQ25oSYYL3NpbdUqY5vfY8WjlnawudFpyJfGrP7Qd2xXs+oY+HTA5L9 HYG+p+V4eBlDcIkQ33/sT8qNfxC8TxPzOExPZE/a5dM+N52o+LuWWB8KjPTdbW+x9UMPeB Qhecxah11hmwDPZRaT9PiF59W4bRSzao28f6nvWfzVCtSEvWNU49ziJdfT9UvzUTpIujSw iU/fUi0oEKauswQ54YxEGuXjuFAKJNNr7aF6yW+3HO1ThHWX9cevyrzYYK6akFYkZC0gOW PhIc3r6BCCYQxX/ItYeHQdHgIF9KDMPtMIGn2ZmhijQyiPsPDfQXidzI/a9xkA== From: Miquel Raynal To: Manikandan Muralidharan Cc: , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v8 5/8] nvmem: layouts: add Microchip/SST SFDP EUI layout driver In-Reply-To: <89aa4ac1eee01e3c425c12367f1e036354787ce8.1790847519.git.manikandan.m@microchip.com> (Manikandan Muralidharan's message of "Wed, 14 Oct 2026 12:10:09 +0530") References: <89aa4ac1eee01e3c425c12367f1e036354787ce8.1790847519.git.manikandan.m@microchip.com> User-Agent: mu4e 1.12.12; emacs 30.2 Date: Wed, 14 Oct 2026 10:52:14 +0200 Message-ID: <87fqy8zmtd.fsf@bootlin.com> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Last-TLS-Session-Version: TLSv1.3 Hi, On 14/10/2026 at 12:10:09 +0530, Manikandan Muralidharan wrote: > Add an NVMEM layout that exposes the factory-programmed EUI-48 identifier > from the Microchip/SST vendor SFDP parameter table (e.g. SST26VF064BEUI) > as a "mac-address" cell, for use as a network MAC address. The vendor > table is located at runtime via the SFDP NVMEM device (no offset in DT), > and a read_post_process callback reverses the LSB-first bytes into > canonical MAC order. Binds to an "nvmem-layout" node with compatible > "microchip,sst26vf-sfdp-eui". > > Signed-off-by: Manikandan Muralidharan Mostly minor nits, see below. > --- a/drivers/nvmem/layouts/Makefile > +++ b/drivers/nvmem/layouts/Makefile > @@ -6,4 +6,5 @@ > obj-$(CONFIG_NVMEM_LAYOUTS) +=3D fixed-layout.o > obj-$(CONFIG_NVMEM_LAYOUT_SL28_VPD) +=3D sl28vpd.o > obj-$(CONFIG_NVMEM_LAYOUT_ONIE_TLV) +=3D onie-tlv.o > +obj-$(CONFIG_NVMEM_LAYOUT_SST26VF_SFDP_EUI) +=3D sst26vf-sfdp-eui.o > obj-$(CONFIG_NVMEM_LAYOUT_U_BOOT_ENV) +=3D u-boot-env.o Not sure this is ordered alphabetically, so in general add it at the end. > +/* SFDP header and parameter header, as laid out on the flash. */ > +struct sfdp_header { > + u8 signature[4]; > + u8 minor; > + u8 major; > + u8 nph; > + u8 unused; > +}; > + > +struct sfdp_parameter_header { > + u8 id_lsb; > + u8 minor; > + u8 major; > + u8 length; > + u8 parameter_table_pointer[3]; > + u8 id_msb; > +}; > + > +#define SFDP_SIGNATURE 0x50444653U > + > +#define SFDP_PARAM_HEADER_ID(h) (((h)->id_msb << 8) | (h)->id_lsb) > +#define SFDP_PARAM_HEADER_PTP(h) get_unaligned_le24((h)->parameter_table= _pointer) > + > +/* Microchip (vendor) parameter table identifier: id_msb << 8 | id_lsb. = */ This is not relevant, we saw it just above ^^^^^^^^^^^^^^^^^^^^^^^ > +#define SFDP_MCHP_VENDOR_ID 0x01bf > + > +#define SFDP_MCHP_EUI48_MARKER_OFFSET 0x60 > +#define SFDP_MCHP_EUI48_MARKER 0x30 > +#define SFDP_MCHP_EUI48_OFFSET 0x61 > + > +static int sfdp_eui_read_post_process(void *priv, const char *id, int in= dex, > + unsigned int offset, void *buf, > + size_t bytes) > +{ > + u8 *data =3D buf; > + int i; > + I believe the if against the length is wrong and should be inverted and placed here: if (bytes !=3D ETH_ALEN) return -EINVAL; Since lenght does not change, prefer to bail out early. > + /* SFDP stores the address least-significant octet first; reverse it. */ > + for (i =3D 0; i < bytes / 2; i++) > + swap(data[i], data[bytes - 1 - i]); > + > + if (bytes =3D=3D ETH_ALEN && !is_valid_ether_addr(buf)) Is bytes !=3D ETH_ALEN a valid use case? > + return -EINVAL; > + > + return 0; > +} > + > +static int sfdp_eui_find_vendor_table(struct nvmem_device *nvmem, u32 *p= tp) > +{ > + struct sfdp_parameter_header ph; > + struct sfdp_header hdr; > + int nph, i, ret; > + > + ret =3D nvmem_device_read(nvmem, 0, sizeof(hdr), &hdr); > + if (ret < 0) > + return ret; > + > + if (get_unaligned_le32(hdr.signature) !=3D SFDP_SIGNATURE) > + return -EINVAL; > + > + /* The number of parameter headers (NPH) field is zero-based. */ > + nph =3D hdr.nph; nph =3D hdr.nph + 1 ? > + > + for (i =3D 0; i <=3D nph; i++) { and here the usual i < nph? > + ret =3D nvmem_device_read(nvmem, sizeof(hdr) + i * sizeof(ph), > + sizeof(ph), &ph); > + if (ret < 0) > + return ret; > + > + if (SFDP_PARAM_HEADER_ID(&ph) !=3D SFDP_MCHP_VENDOR_ID) > + continue; > + > + *ptp =3D SFDP_PARAM_HEADER_PTP(&ph); > + return 0; > + } > + > + return -ENOENT; > +} ... > + info.name =3D "mac-address"; > + info.offset =3D base + SFDP_MCHP_EUI48_OFFSET; > + info.bytes =3D ETH_ALEN; > + info.np =3D of_get_child_by_name(layout_np, "mac-address"); > + info.read_post_process =3D sfdp_eui_read_post_process; > + > + ret =3D nvmem_add_one_cell(nvmem, &info); > + if (ret) > + of_node_put(info.np); > + else > + dev_dbg(dev, "exposed EUI-48 at SFDP offset 0x%x\n", info.offset); This one is not really useful anymore. > + > + of_node_put(layout_np); > + > + return ret; > +} > + Thanks, Miqu=C3=A8l