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mmc: core: Set non-default Drive Strength via platform hook

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Non default Drive Strength cannot be set automatically.  It is a function
of the board design and only if there is a specific platform handler can
it be set.  The platform handler needs to take into account the board
design.  Pass to the platform code the necessary information.

For example:  The card and host controller may indicate they support HIGH
and LOW drive strength.  There is no way to know what should be chosen
without specific board knowledge.  Setting HIGH may lead to reflections
and setting LOW may not suffice.  There is no mechanism (like ethernet
duplex or speed pulses) to determine what should be done automatically.

If no platform handler is defined -- use the default value.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Reviewed-by: Arindam Nath <arindam.nath@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>
This commit is contained in:
Philip Rakity 2011-07-06 08:51:32 -07:00 • committed by Chris Ball
commit ca8e99b32e
2 changed files with 40 additions and 29 deletions
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include/linux/mmc/host.h
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@ -148,6 +148,7 @@ struct mmc_host_ops {
int (*start_signal_voltage_switch)(struct mmc_host *host, struct mmc_ios *ios);
int (*execute_tuning)(struct mmc_host *host);
void (*enable_preset_value)(struct mmc_host *host, bool enable);
int (*select_drive_strength)(unsigned int max_dtr, int host_drv, int card_drv);
};
struct mmc_card;