On Thu, 21 Oct 2010, Philip Rakity wrote:
>
> Sometimes it is useful for the SD driver to know the type of card that is in use so that dynamic sd bus clocking can be enabled or disabled.
> Dynamic clocks are a feature of sd 3.0 and we can support this in our v2.0 controller.
>
> The problem is that some SDIO cards are not happy when the clocks are dynamically stopped. I have not seen any issues with SD/mmc/eMMC cards. I suspect the reason for the SDIO problems is that the cards need the clock since SDIO cards can interrupt the CPU for service and the other card types cannot.
>
> The information about the type of card being used is known by the mmc layer when
>
> mmc_alloc_card(struct mmc_host *host, struct device_type *type) --- core/bus.c
>
> is called but the sd driver cannot get to this information when set_ios() is called by the mmc layer since the host->card field is filled in too late.
>
> I have added host->card = card to
>
> struct mmc_card *mmc_alloc_card(struct mmc_host *host, struct device_type *type)
> {
> struct mmc_card *card;
>
> card = kzalloc(sizeof(struct mmc_card), GFP_KERNEL);
> if (!card)
> return ERR_PTR(-ENOMEM);
>
> card->host = host;
>
> device_initialize(&card->dev);
>
> card->dev.parent = mmc_classdev(host);
> card->dev.bus = &mmc_bus_type;
> card->dev.release = mmc_release_card;
> card->dev.type = type;
> + host->card = card;
> return card;
> }
>
> and this works for me provided the sd driver remembers to check for card being NULL in the driver specific set_clock code.
>
> My pseudo code is
>
> if (host->mmc->card == NULL)
> dynamic_clocks=FALSE;
> else if host->mmc->card == MMC_TYPE_SDIO)
> dynamic_clocks = TRUE;
> else
> dynamic_clocks = FALSE;
>
>
> My question is: Is there a better way to pass the type of card to the sd driver?
I don't like this. Again we should strive to make the controller driver
as simple as possible and let the core code handle this kind of clocking
logic as much as possible. The OMAP driver is again a terribly bad
example to follow.
If there are cases where the clock still has to remain active with some
cards, it is far better to take care of such exceptions in only one
place instead of having to add a card quirk in every controller drivers.
The controller driver should remain card agnostic as much as possible
and not take decisions on its own based on card type.
Stopping the clock would also be a good thing even for those controllers
without dynamic clock support. The core could certainly stop the clock
manually after a period of inactivity for example.
So if your controller hardware has the ability to dynamically stop the
clock on its own, then the driver should simply expose that knowledge to
the core with a capability bit, and the core should tell the driver to
enable that mode through mmc_set_ios() when applicable.
Nicolas
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