On 21 August 2012 21:31, Rob Herring [off-list ref] wrote:

On 08/21/2012 10:18 AM, Chris Ball wrote:

quoted

Hi,

On Tue, Aug 21 2012, Rob Herring wrote:

quoted

quoted

cd-gpios and cd-external can be present on the same node.  if broken-cd
is present, it must be the only one of these nodes used.

I don't see the point of cd-external. Either you just use the CD
interrupt defined within the SDHCI or you have a gpio line independent
of the SDHCI and use cd-gpios.

You've described two of the possible cases, but not the third.  In the
third case, you have a gpio line that is not independent of the SDHCI,
because it is the SDHCI's CD pin brought out to be directly accessible
via a GPIO.

That is covered by absence of cd-gpios and broken-cd. Any *-gpios
property means the signal is a GPIO line controlled by a GPIO controller.

I suppose you could have the CD state readable via the SDHCI, but the
interrupt comes from a GPIO controller. Or vice-versa, but that's a
pretty broken use case if you can't pick which way you are going to use
things.

quoted

The difference is in the handling of the interrupt -- if you don't have
"cd-external" then you're just using the SDHCI's interrupt, but if you
have an independent line then you're going to need to register your own
IRQ handler on it, and "cd-external" signifies that.

Thomas wrote this explanation earlier in the thread:

quoted

"samsung,sdhci-cd-gpio" means that the cd-gpio line is not connected
to the card-detect pad of the sdhci controller. Instead, it identifies
cd-gpio as a gpio pin, connected to the card-detect pin of the "card
slot" and it can used as a source of external interrupt. The driver
can register card insert/remove handler for this interrupt and get
notified about the changes in card state.

"sdhci-cd-internal" means that the "cd-gpio" line is used to connect
the card-detect pin of the card slot and the card-detect pad of the
sdhci controller. The controller is then aware of any changes in card
state and the controller generates appropriate interrupts to notify
changes in card-state.

It seems you are mixing pin muxing and who controls/handles the CD
detect signal. Pin muxing is a separate issue and should be addressed by
pin mux bindings. Either the signal functions as a GPIO or it functions
as a CD as part of the SDHCI. You may have muxing on the CD pin that
allows it to function either way, but the DT binding should describe how
you want it to be configured and used.

Ok, I agree with Rob. I was mixing pin muxing here. So if we have
'cd-gpios' and 'broken-cd' as generic bindings, would the following be
valid?

[A] cd-gpios not present ,  broken-cd not present : This means that
there is no card detect pin available. Controller drivers are free to
infer this as "card detection is broken" and use implementation
specific behavior.

[B] cd-gpio not present , broken-cd present :  This means that there
is nothing connected to the card-detect pad of the mmc host
controller. Controller drivers are free to use implementation specific
behavior to deal with card detection.

[C] cd-gpio present, broken-cd not present : This means that 'cd-gpio'
line connects card-detect pad of the controller to the card-detect pin
of the mmc slot.

[D] cd-gpio present, broken-cd present : This means that there is
nothing connected to the card-detect pad of the mmc host controller.
Controller drivers are free to use the 'cd-gpio' line in any
implementation specific way.

Thanks,
Thomas.