Some Older AMD Systems Can Boot Faster On Linux 5.17+
Written by Michael Larabel in AMD on 18 January 2022 at 05:19 AM EST. 7 Comments
AMD --
A change merged overnight with the libata subsystem updates for Linux 5.17 means that some older AMD hardware will be able to boot quicker by avoiding an otherwise mandated sleep period.

Merged this morning were the ATA subsystem updates for Linux 5.17. Usually the ATA changes don't amount to many noteworthy changes but "Add support for AMD A85 FCH (Hudson D4) AHCI adapters" got my attention... Yeah, the chipset from the early AMD "Fusion" APU days.

What that support change is about is adding the AMD A85 Hudson D4 chipset to the AHCI driver code so it can apply a quirk/workaround.

Within the libata SATA driver code there is a forced 200ms delay with an accompanying code comment, "Some PHYs react badly if SStatus is pounded immediately after resuming. Delay 200ms before debouncing." But the 200 ms delay can be noticeable if the system is otherwise fast at booting. For those still using an AMD A85 FCH (Hudson D4) it's been deemed safe to skip this 200 ms debounce delay in the SATA link resume code.

For now the AMD A85 Hudson D4 is the only chipset listed while hopefully other hardware can be added when deemed safe and now that this "board_ahci_no_debounce_delay" has been added to the AHCI code.


The commit mentions the difference for the developer who tracked down the boot time slowdown, "On the ASUS F2A85-M PRO it reduces the Linux kernel boot time by the expected 200 ms from 787 ms to 585 ms." This is far from the first time we have seen Linux kernel boot time optimizations come by avoiding arbitrary delays catering to select hardware.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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