On Mon, Nov 09, 2015 at 05:00:46PM +0100, Ulf Hansson wrote: > 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. > Yes but I don't know if we are doing something weird/wrong or if it is the naming of the 'SD Bus Voltage Select' which is weird/wrong. > 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? :-) There is this discussion because of two things: - Fixing something I consider as a bug: when I have a VMMC, only setting/clearing bit 0. Our controller strictly obeys to the spec and check the 'SD Bus Voltage Select' field. Since we put a reserved value (000), the Power On is not performed. - I was trying to get help to understand what is this 'SD Bus Voltage'. For our controller and sdhci_set_power(), it seems to stand for VMMC. For me, everything concerning bus voltage is related to VQMMC, so I was disappointed. Regards Ludovic -- 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
