Re: [PATCH 2/2] mmc: Add mmc_force_detect_change_begin / _end functions

[Hans de Goede]

Hi,

On 21-07-17 16:35, Quentin Schulz wrote:
> From: Hans de Goede <hdegoede@xxxxxxxxxx>
>
> Some sdio devices have a multiple stage bring-up process. Specifically
> the esp8089 (for which an out of tree driver is available) loads firmware
> on the first call to its sdio-drivers' probe function and then resets
> the device causing it to reboot from its RAM with the new firmware.
>
> When this sdio device reboots it comes back up in 1 bit 400 KHz mode
> again, and we need to walk through the whole ios negatiation and sdio setup
> again.
>
> There are 2 problems with this:
>
> 1) Typically these devices are soldered onto some (ARM) tablet / SBC
> PCB and as such are described in devicetree as "non-removable", which
> causes the mmc-core to scan them only once and not poll for the device
> dropping of the bus. Normally this is the right thing todo but in the
> eso8089 example we need the mmc-core to notice the module has disconnected
> (since it is now in 1 bit mode again it will not talk to the host in 4 bit
> mode). This can be worked around by using "broken-cd" in devicetree
> instead of "non-removable", but that is not a proper fix since the device
> really is non-removable.
>
> 2) When the mmc-core detects the device has disconnected it will poweroff
> the device, causing the RAM loaded firmware to be lost. This can be worked
> around in devicetree by using regulator-always-on (and avoiding the use of
> mmc-pwrseq), but again that is more of a hack then a proper fix.
>
> This commmit fixes 1) by adding a mmc_force_detect_change function which
> will cause scanning for device removal / insertion until a new device is
> detected. 2) Is fixed by a keep_power flag to the mmc_force_detect_change
> function which when set causes the mmc-core to keep the power to the device
> on during the rescan.
>
> Cc: Icenowy Zheng <icenowy@xxxxxxxx>
> Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>
> Cc: Chen-Yu Tsai <wens@xxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>

So when I posted this patch quite a while back, there was some discussion
about this and a consensus that this is not the right solution.

So first of all lets describe the problem:

The esp8089 sdio wifi chip is really an ARM core with a wifi phy
connected to it (as many wifi chipsets are).

But this one comes up in some really generic sdio capable boot-loader
mode and we need to feed it firmware and then reboot it into the
new firmware.

The reboot is where the problems happens. It seems to fallback
from the negotiated 4 wire sdio mode to single wire spi mode then.

The out of tree version of the driver deals with this by not setting
the non-removable flag as well as setting the broken_cd flag so that
the mmc core polls the device, after the reboot the poll fails
because the mmc-controller and the esp8089 are using a different
amount of wires so the mmc-cmd the poll uses times out.

After which the esp8089 drivers remove function gets called, and
the mmc stack re-discovers the esp8089 by restarting the whole
number of wires (and speed) used negotiation. After which the
esp8089 driver's probe function gets called (again) and on
firmware loading is has set a global flag, so now it actually
acts as a wifi driver rather then trying to load the firmware
a second time.

Since I did not want to rely on broken_cd polling I came up
with the hack which is this patch.

So when this patch was first discussed we came to the conclusion
that what we really need is some sort of mmc_reprobe_device
function which the driver can call from probe which will
redo the number of wires (and speed) used negotiation,
while keeping the sdio_function device as is so that probe can
simply continue after this and we also don't need the ugly
global flag.

The idea would be for this function to be some wrapper
around mmc_init_card() which resets the ios settings as is
normally done on remove and then call mmc_init_card()
passing in the existing card the same way as is done
one resume, so that the existing card / sdio_function
devices get reused.

IIRC Ulf would look into writing this mmc_reprobe_device
function and then I would test it with the esp8089, but
Ulf never got around to writing the function and I ended
up working on other things too.

I HTH.

Regards,

Hans





> ---
>   drivers/mmc/core/core.c  | 47 ++++++++++++++++++++++++++++++++++++++++++-----
>   include/linux/mmc/host.h |  7 +++++++
>   2 files changed, 49 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 26431267a3e2..103badde910b 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1620,8 +1620,11 @@ int mmc_select_drive_strength(struct mmc_card *card, unsigned int max_dtr,
>    */
>   void mmc_power_up(struct mmc_host *host, u32 ocr)
>   {
> -	if (host->ios.power_mode == MMC_POWER_ON)
> +	if (host->ios.power_mode == MMC_POWER_ON) {
> +		if (host->ios.clock == 0)
> +			goto set_clock;
>   		return;
> +	}
>   
>   	mmc_pwrseq_pre_power_on(host);
>   
> @@ -1646,6 +1649,7 @@ void mmc_power_up(struct mmc_host *host, u32 ocr)
>   
>   	mmc_pwrseq_post_power_on(host);
>   
> +set_clock:
>   	host->ios.clock = host->f_init;
>   
>   	host->ios.power_mode = MMC_POWER_ON;
> @@ -1663,6 +1667,11 @@ void mmc_power_off(struct mmc_host *host)
>   	if (host->ios.power_mode == MMC_POWER_OFF)
>   		return;
>   
> +	if (host->rescan_keep_power) {
> +		mmc_set_clock(host, 0);
> +		return;
> +	}
> +
>   	mmc_pwrseq_power_off(host);
>   
>   	host->ios.clock = 0;
> @@ -1804,6 +1813,27 @@ void mmc_detect_change(struct mmc_host *host, unsigned long delay)
>   }
>   EXPORT_SYMBOL(mmc_detect_change);
>   
> +/**
> + *	mmc_force_detect_change - force rescanning of a MMC socket even if
> + *				  it is non-removable
> + *	@host: host to rescan
> + *	@delay: optional delay to wait before detection (jiffies)
> + *	@keep_power: if set do not turn of vdd / call pwrseq_off during rescan
> + *
> + *	MMC drivers which need non-removable sdio devices to be rescanned
> + *	(e.g. because the device reboots its fw after a firmware upload),
> + *	can call this to force scanning the MMC socket for changes, even
> + *	if it is non-removable.
> + */
> +void mmc_force_detect_change(struct mmc_host *host, unsigned long delay,
> +			     bool keep_power)
> +{
> +	host->rescan_force = 1;
> +	host->rescan_keep_power = keep_power;
> +	_mmc_detect_change(host, delay, false);
> +}
> +EXPORT_SYMBOL(mmc_force_detect_change);
> +
>   void mmc_init_erase(struct mmc_card *card)
>   {
>   	unsigned int sz;
> @@ -2566,7 +2596,8 @@ void mmc_rescan(struct work_struct *work)
>   		return;
>   
>   	/* If there is a non-removable card registered, only scan once */
> -	if (!mmc_card_is_removable(host) && host->rescan_entered)
> +	if (!mmc_card_is_removable(host) && host->rescan_entered &&
> +	    !host->rescan_force)
>   		return;
>   	host->rescan_entered = 1;
>   
> @@ -2583,7 +2614,8 @@ void mmc_rescan(struct work_struct *work)
>   	 * if there is a _removable_ card registered, check whether it is
>   	 * still present
>   	 */
> -	if (host->bus_ops && !host->bus_dead && mmc_card_is_removable(host))
> +	if (host->bus_ops && !host->bus_dead &&
> +	    (mmc_card_is_removable(host) || host->rescan_force))
>   		host->bus_ops->detect(host);
>   
>   	host->detect_change = 0;
> @@ -2616,15 +2648,20 @@ void mmc_rescan(struct work_struct *work)
>   	}
>   
>   	for (i = 0; i < ARRAY_SIZE(freqs); i++) {
> -		if (!mmc_rescan_try_freq(host, max(freqs[i], host->f_min)))
> +		if (!mmc_rescan_try_freq(host, max(freqs[i], host->f_min))) {
> +			if (host->rescan_force) {
> +				host->rescan_force = 0;
> +				host->rescan_keep_power = 0;
> +			}
>   			break;
> +		}
>   		if (freqs[i] <= host->f_min)
>   			break;
>   	}
>   	mmc_release_host(host);
>   
>    out:
> -	if (host->caps & MMC_CAP_NEEDS_POLL)
> +	if ((host->caps & MMC_CAP_NEEDS_POLL) || host->rescan_force)
>   		mmc_schedule_delayed_work(&host->detect, HZ);
>   }
>   
> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
> index ebd1cebbef0c..d56d79867bbd 100644
> --- a/include/linux/mmc/host.h
> +++ b/include/linux/mmc/host.h
> @@ -338,6 +338,8 @@ struct mmc_host {
>   
>   	int			rescan_disable;	/* disable card detection */
>   	int			rescan_entered;	/* used with nonremovable devices */
> +	int			rescan_force;	/* force rescan of (nonremovable) devices */
> +	int			rescan_keep_power; /* Do not power off card */
>   
>   	int			need_retune;	/* re-tuning is needed */
>   	int			hold_retune;	/* hold off re-tuning */
> @@ -420,6 +422,11 @@ int mmc_power_save_host(struct mmc_host *host);
>   int mmc_power_restore_host(struct mmc_host *host);
>   
>   void mmc_detect_change(struct mmc_host *, unsigned long delay);
> +
> +/* HdG: HACK HACK HACK do not upstream */
> +#define MMC_HAS_FORCE_DETECT_CHANGE
> +void mmc_force_detect_change(struct mmc_host *host, unsigned long delay,
> +			     bool keep_power);
>   void mmc_request_done(struct mmc_host *, struct mmc_request *);
>   void mmc_command_done(struct mmc_host *host, struct mmc_request *mrq);
>