I'm running LUbuntu 18.04 on a Lenovo T450s. The SD card is usually recognized just fine when it is inserted into the slot, but sometimes, inexplicably, I will insert a card and nothing will happen. I don't see any messages in dmesg, no error message, no indication of any kind that I did anything. If I reboot it seems to clear the problem up, especially if the card is already in the slot - although this is inconvenient because then I have to get everything back to where it was when I was ready to read files off the card.
I'm not 100% sure, but I have read that the SD card reader on this system is PCI based. Is there some command I can run to diagnose and possibly fix this issue when it occurs without the need for a reboot?