On Oct 21, 2010, at 9:57 AM, Nicolas Pitre wrote:
> 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.
Not looking at OMAP
>
> 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.
Was not going to add a quirk. The low level platform specific code for
sdhci.c can handle this if it knows the card type. It can program the
appropriate hardware registers.
>
> 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.
agree except that stopping the clock for SDIO cards is not a good thing to do
in our experience.
if the core can signal this via set_ios this works for me. This is why I
suggested the code telling
set_ios the card type which allowed the platform specific code to enable or not
dynamic
clocks.
>
> 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.
sd 3.0 spec (not marvell specific) suppports dynamic clocking as well as
marvell v2.0
controller.
I can add a CAP bit -- but for SDIO cards we will certainly set this to not
disable the clocks.
100,000 foot summary
a) add new mmc->caps bit indicating dynamic clocks can be supported in the
controller
b) add new field in ios that indicates if clocks should be dynamic
c) pass this to set_ios
d) add platform specific hook to set_ios to control the dynamic clocking option.
Is my understanding correct ?
>
>
> Nicolas
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