Hi, The XO-1.5 laptop ships with an internal wifi adapter connected to the SDIO bus (on a sdhci-pci host). We were experiencing a problem where initialization of this card sometimes failed (on low-level SD stuff, like setting voltage or reading CCCR). Also, when runtime PM was enabled, the card consistently fails to come back after it has been powered down. We believe this is due to a hardware bug with the wifi card. After SD power has been cut and restored, the card is left in inconsistent state. http://dev.laptop.org/ticket/10270#comment:4 "According to a confidential Marvell AN, we should be asserting RESET externally after powering up the WLAN card. The Linux driver should assert WLAN_RESETn low for between 1 and 20 uS, about 1 mS after turning on power to the card" While other users of this wifi card have WLAN_RESETn permanently wired low, OLPC has it wired to a GPIO. So we *can* do the above from the kernel, but its specific to this particular laptop. The question is: how? The actual code to do this is trivial, but where would we fit it into the kernel? Ohad suggested that we look at the regulator subsystem. After having a look I think this would be a hack at best. The docs say: "The intention is to allow systems to dynamically control regulator power output in order to save power and prolong battery life. This applies to both voltage regulators (where voltage output is controllable) and current sinks (where current limit is controllable)." And indeed, the requirement that you're regulating current or voltage comes all the way into the implementation. In this case we are not changing current or voltage, we are just asserting a specific signal to the card. So its messy from the start (I'd have to invent a list of supported voltages or something). Another option would be just to hack this into the kernel. Inside mmc_power_up we'd add something like the following: #ifdef CONFIG_OLPC if (machine_is_olpc()) olpc_reset_gpio_fixup(host); #endif And olpc_reset_gpio_fixup() would check that we're running on XO-1.5, check that the host in question is the one where the wifi card is, and do the GPIO twiddle. Another cleaner option (but perhaps OTT for just 1 user?) would be to add a notifier chain that is called at this point. Then we'd add a whole new "driver" in drivers/mmc somewhere that registers the appropriate notifier and handles this case. Thoughts? Other ideas? Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
