AZL-56816

In the Linux kernel, the following vulnerability has been resolved:

serial: sc16is7xx: convert from raw to noinc regmap functions for FIFO

The SC16IS7XX IC supports a burst mode to access the FIFOs where the initial register address is sent ($00), followed by all the FIFO data without having to resend the register address each time. In this mode, the IC doesn't increment the register address for each R/W byte.

The regmaprawread() and regmaprawwrite() are functions which can perform IO over multiple registers. They are currently used to read/write from/to the FIFO, and although they operate correctly in this burst mode on the SPI bus, they would corrupt the regmap cache if it was not disabled manually. The reason is that when the R/W size is more than 1 byte, these functions assume that the register address is incremented and handle the cache accordingly.

Convert FIFO R/W functions to use the regmap noinc versions in order to remove the manual cache control which was a workaround when using the raw versions. FIFO registers are properly declared as volatile so cache will not be used/updated for FIFO accesses.