On 9 November 2015 at 15:40, Ludovic Desroches <ludovic.desroches@xxxxxxxxx> wrote: > On Mon, Nov 09, 2015 at 03:12:46PM +0100, Ulf Hansson wrote: >> On 9 November 2015 at 14:23, Ludovic Desroches >> <ludovic.desroches@xxxxxxxxx> wrote: >> > On Fri, Nov 06, 2015 at 04:59:29PM +0100, Ludovic Desroches wrote: >> >> When there is a vmmc regulator, only SD Bus Power is set to 1 in the >> >> Power Control Register. It means SD Bus Voltage Select field is set to 0 >> >> that is a reserved value. The SD Host Controller specification says: >> >> 'SD Bus Power: Before setting this bit, the SD Host Driver shall set SD >> >> Bus Voltage Select.' and 'If the Host Driver selects an unsupported >> >> voltage in the SD B?us Voltage Select field, the Host Controller may >> >> ignore writes to SD Bus Power and keep its value at zero." >> >> >> >> Having an external regulator means the SD Bus Voltage Select is useless >> >> but if the Host Controller strictly follows the specification then we >> >> need to set a valid value. >> > >> > Ulf, >> > >> > What is your opinion about this patch? >> > >> > If the 'no regulator found' message is turned in debug message, I can get >> > rid of my vmmc regulator but I really think that writing only >> >> I expect you mean vqmmc? > > I don't mean vmmc. In the sdhci_set_power function, we are using vmmc. > I feel not confortable with it because the power control register > contains 'SD Bus' fields so it should depend on vqmmc not vmmc. > >> >> > SDHCI_POWER_ON is opposite to the sdhci spec. I would say that not >> > setting the bus voltage is a quirk! >> >> I don't really follow. >> >> I read the SDHCI spec and the section for the Power Control Register. >> Bit 0 needs to be set when communicating with the card as it will for >> example enables the clock. Before setting bit0 you must decide what >> signal level to use, which is done by writing to bit 1->3. >> > > Right. But when having vmmc supply we do: > sdhci_writeb(host, SDHCI_POWER_ON, SDHCI_POWER_CONTROL) or > sdhci_writeb(host, 0, SDHCI_POWER_CONTROL) so we loose the signal level, > isn't it? > >> If SDHCI monitors the power state (MMC_POWER_UP|ON|OFF) when its >> ->set_ios() callback are invoked and in combination of using the >> ->start_signal_voltage_switch() callback to change the signal voltage >> level, this *should* work out nicely. >> > > It is my turn to not follow! We write into the Power Control Register > only in sdhci_set_power(). May I miss a callback or something else? > sdhci_do_start_signal_voltage_switch doesn't modify the Power Control > Register. > >> Now, looking at the related code in sdhci, I am kind of surprised that >> it works. :-) Though, again I don't have the in-depth knowledge about >> sdhci. >> > > Me too, I am starting to dig into the sdhci spec and some points are > not crystal clear. > Okay, I am finally starting to understand some of your concern. According to the spec, the Power Control Register should control the signal voltage/bus voltage. As UHS mode was added to the spec, it seems like the Power Control Register couldn't cover all new cases, as why Host Control 2 register needed to be added. The Host Control 2 register, is what sdhci_do_start_signal_voltage_switch() uses to change the signal voltage level, which all makes sense to me. For sdhci_set_power(); it seems to use the Power Control Register to control the power to the card (VDD/VMMC). Indeed this looks *really* weird/wrong. I wonder if it's working because of luck, intentional violation of the SDHCI spec or because of special variants. Especially when looking into the case when you *don't* have a VMMC regulator several strange quirks exists in sdhci_set_power(). In the case when you *have* a VMMC, I think just setting/clearing bit 0 (SDHCI_POWER_ON) and then bail out, is probably working with modern HW because it's likely the only thing needed. Now, this discussion was interesting, but I forgot what problem you actually where trying to solve? :-) Kind regards Uffe -- 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
