Re: [Regression Resend] mmc: mx28: sd card detection broken since 3.18-rc1

[Michael Heimpold <mhei@heimpold.de>]

Hi Kristina,

Am Montag, 3. November 2014, 23:50:53 schrieb Kristina Martšenko:
> On 03/11/14 22:49, Michael Heimpold wrote:
> > Hi,
> 
> Hi Michael,
> 
> > Am Montag, 3. November 2014, 01:01:07 schrieben Sie:
> >> On 01/11/14 23:40, Stefan Wahren wrote:
> >>> Hi,
> >>>
> >>> i was testing Linux Kernel 3.18-rc2 with my i.MX28 board (I2SE Duckbill) and ran
> >>> into the problem that the sd card isn't detected from the Kernel at booting
> >>> (driver: mxs-mmc.c). That results in a endless wait for the root partition
> >>
> >> I ran into this issue as well. Seems that a card-detect flag 
> >> (MMC_CAP2_CD_ACTIVE_HIGH) can currently be set based on an 
> >> uninitialized variable, which can lead to the card being reported as 
> >> not present. This patch fixes it for me:
> >>
> >> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> >> index 03c53b72a2d6..f0e187682d3b 100644
> >> --- a/drivers/mmc/core/host.c
> >> +++ b/drivers/mmc/core/host.c
> >> @@ -311,7 +311,7 @@ int mmc_of_parse(struct mmc_host *host)
> >>  	struct device_node *np;
> >>  	u32 bus_width;
> >>  	int len, ret;
> >> -	bool cap_invert, gpio_invert;
> >> +	bool cap_invert, gpio_invert = false;
> >>  
> > 
> > sorry, but I don't understand how your patch fixes the problem.
> > 
> > First use of the gpio_invert bool is in line 370/371 within mmc_gpiod_request_cd
> > (re-wrapped into a single line here for better reading):
> > 
> > -snip-
> > ret = mmc_gpiod_request_cd(host, "cd", 0, true,  0, &gpio_invert);
> > -snap-
> > 
> > A pointer to the bool is passed, and inside mmc_gpiod_request_cd (drivers/mmc/core/slot-gpio.c,
> > line 322), always a value is assigned:
> > 
> > -snip-
> > if (gpio_invert)
> >                 *gpio_invert = !gpiod_is_active_low(desc);
> > -snap-
> > 
> > So returning to mmc_of_parse, the bool should always have an initialized value.
> > Apart from some error handling, the bool is used immediately in the xor expression
> > and results in setting MMC_CAP2_CD_ACTIVE_HIGH bit, or not.
> > 
> > I also cannot see a code path, where gpio_invert is used without a call to mmc_gpiod_request_cd.
> > 
> > Would be nice, if you could point me to what I'm missing.
> 
> mmc_gpiod_request_cd can return without ever reaching the line where 
> the value is assigned to gpio_invert:
> 
> desc = devm_gpiod_get_index(host->parent, con_id, idx, GPIOD_IN);
> if (IS_ERR(desc))
> 	return PTR_ERR(desc);
> 
> This can happen when the host controller doesn't use a GPIO for card 
> detection (but instead uses a dedicated pin). In this case 
> devm_gpiod_get_index will return -ENOENT.
> 

ah, I see - thank you for taking the time to explain.

> >>  	if (!host->parent || !host->parent->of_node)
> >>  		return 0;
> >> @@ -401,6 +401,7 @@ int mmc_of_parse(struct mmc_host *host)
> >>  	else
> >>  		cap_invert = false;
> >>  
> >> +	gpio_invert = false;
> >>  	ret = mmc_gpiod_request_ro(host, "wp", 0, false, 0, &gpio_invert);
> > 
> > Same here. The functions always assigns a value when a pointer is given.
> 
> Same thing, the function can return before gpio_invert is ever assigned 
> to.
> 
> > (And this change is unrelated to the reporters problem, so should be fixed with a
> > dedicated patch.)
> 
> Since both flags are set wrong for the exact same reason, and they're 
> both regressions in 3.18, I thought it would make sense to fix them 
> both in one patch. (Especially since I think it's cleaner to split the 
> gpio_invert variable into cd_gpio_invert and ro_gpio_invert, and I was 
> going to do that in the patch I'd send.) Let me know if you still think 
> I should send separate patches for them.
 
Splitting the variable sounds good to me and will improve readability. In this case
(and with proper commit message) I think it's really possible to combine both fixes
in one patch.

Thanks,
Michael

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