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The workaround for VSOL V2801F brand based GPON SFP modules added in commit0d035bed2a("net: sfp: VSOL V2801F / CarlitoxxPro CPGOS03-0490 v2.0 workaround") works only for IDs added explicitly to the list. Since there are rebranded modules where OEM vendors put different strings into the vendor name field, we cannot base workaround on IDs only. Moreover the issue which the above mentioned commit tried to work around is generic not only to VSOL based modules, but rather to all GPON modules based on Realtek RTL8672 and RTL9601C chips. These include at least the following GPON modules: * V-SOL V2801F * C-Data FD511GX-RM0 * OPTON GP801R * BAUDCOM BD-1234-SFM * CPGOS03-0490 v2.0 * Ubiquiti U-Fiber Instant * EXOT EGS1 These Realtek chips have broken EEPROM emulator which for N-byte read operation returns just the first byte of EEPROM data, followed by N-1 zeros. Introduce a new function, sfp_id_needs_byte_io(), which detects SFP modules with broken EEPROM emulator based on N-1 zeros and switch to 1 byte EEPROM reading operation. Function sfp_i2c_read() now always uses single byte reading when it is required and when function sfp_hwmon_probe() detects single byte access, it disables registration of hwmon device, because in this case we cannot reliably and atomically read 2 bytes as is required by the standard for retrieving values from diagnostic area. (These Realtek chips are broken in a way that violates SFP standards for diagnostic interface. Kernel in this case simply cannot do anything less of skipping registration of the hwmon interface.) This patch fixes reading of EEPROM content from SFP modules based on Realtek RTL8672 and RTL9601C chips. Diagnostic interface of EEPROM stays broken and cannot be fixed. Fixes:0d035bed2a("net: sfp: VSOL V2801F / CarlitoxxPro CPGOS03-0490 v2.0 workaround") Co-developed-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> Signed-off-by: Pali Rohár <pali@kernel.org> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.