Hi Jakob, On 6/25/26 1:55 PM, Jakob Unterwurzacher wrote:
From: Jakob Unterwurzacher <[email protected]>As it is, an NVMe's built-in PERSTN pull-up fights against the SoC's built-in pull-down which results in an undefined logic state on the Samsung SSD 980 and likely others. Fix that by forcing PERSTN low as early as possible, which is SPL. Both Linux and U-Boot (via "pci enum") set the pin high later as needed and the NVMe is detected fine. Oscillocope shots ("x" means undefined logic state at around 1.5V): Before: 3V3 ____|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ PERSTN ____xxxxxxxxxxxxxxx_|‾‾‾‾‾ PCICLK ____∿∿∿∿∿∿∿∿∿∿∿∿___∿∿∿∿∿∿∿ ^U-Boot ^ Linux After: 3V3 ____|‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ PERSTN ____x_______________|‾‾‾‾‾ PCICLK ____∿∿∿∿∿∿∿∿∿∿∿∿___∿∿∿∿∿∿∿ ^U-Boot ^ Linux With this change, the power-up sequence conforms to PCIe specs, except a remaining short PERSTN glitch. The glitch is about 400ms long. It could be shortened by moving the logic to TPL, but completely fixing it is only possible in hardware. Signed-off-by: Jakob Unterwurzacher <[email protected]>
Reviewed-by: Quentin Schulz <[email protected]> Thanks! Quentin
