PCI rescan needed for MMC reader to become usable

Hi:

My laptop's card reader (dell xps 15z uses driver jmb38x_ms, kernel 3.8-rc2 or older no difference) does nothing unless:

a) An SD card is plugged into the slot before powering the machine on.

b) I plug the card and run echo 1 > /sys/bus/pci/rescan

then the device appears

[ 2154.277991] jmb38x_ms 0000:05:00.3: enabling device (0000 -> 0002)
[ 2154.280299] sdhci: Secure Digital Host Controller Interface driver
[ 2154.280301] sdhci: Copyright(c) Pierre Ossman
[ 2154.281171] sdhci-pci 0000:05:00.0: SDHCI controller found [197b:2392] (rev 30)
[ 2154.281184] sdhci-pci 0000:05:00.0: enabling device (0000 -> 0002)
[ 2154.303986] mmc0: SDHCI controller on PCI [0000:05:00.0] using DMA
[ 2154.304025] sdhci-pci 0000:05:00.2: SDHCI controller found [197b:2391] (rev 30)
[ 2154.304038] sdhci-pci 0000:05:00.2: enabling device (0000 -> 0002)
[ 2154.304050] sdhci-pci 0000:05:00.2: Refusing to bind to secondary interface.
[ 2154.573690] mmc0: new SDHC card at address e624
[ 2154.576527] mmcblk0: mmc0:e624 SU04G 3.69 GiB
[ 2154.586277]  mmcblk0: p1

After that there is no problem.

Can anyone point to a possible cause of this problem ? (cc your replies please)