[U-Boot] [PATCH v2 26/29] dm: Add child_pre_probe() and child_post_remove() methods

[Pavel Herrmann]

Hi

On Tuesday 08 of July 2014 21:38:16 Simon Glass wrote:
> ...
> +
> +Note that the information that controls this behaviour is in the bus's
> +driver, not the child's. In fact it is possible that child has no knowledge
> +that it is connected to a bus. The same child device may even be used on
> two +different bus types. As an example. the 'flash' device shown above may
> also +be connected on a SATA bus or standalone with no bus:
> +
> +   xhci_usb (UCLASS_USB)
> +      flash (UCLASS_FLASH_STORAGE)  - parent data/methods defined by USB
> bus +
> +   sata (UCLASS_SATA)
> +      flash (UCLASS_FLASH_STORAGE)  - parent data/methods defined by SATA
> bus +
> +   flash (UCLASS_FLASH_STORAGE)  - no parent data/methods (not on a bus)

this is not the best example, since the driver actually needs to have an idea 
what parent bus it is connected to, as it should use the parents driver.ops to 
communicate with the device.

the better (more realistic) version would show that the same device would 
operate under various xhci_usb, ohci_usb and ehci_usb busses, which might very 
well have different parent_priv structure (for example, ohci_usb would probably 
not store maximum speed supported by the device, since the bus only has the 
basic one)

as a side note, flash is a bit tricky here, since USB and SATA do not provide 
you with "flash-like" interface even for flash-based devices, but instead have a 
disk-like interface, which is simpler (does not give you the ability to 
control bad block management, among other things).


regards
Pavel Herrmann