[PATCH] mini2440 MMC correct write protect detection

[krzk@kernel.org (Krzysztof Kozlowski)]

On Wed, Sep 05, 2018 at 09:45:15PM +0200, Cedric Roux wrote:
> On 09/05/2018 07:45 PM, Krzysztof Kozlowski wrote:
> > I looked at Mini2440 schematics found on the net and it looks like the
> > pin (just like CD) is active low. However I might be looking at wrong
> > schematics or missing some things.
> 
> I have the same schematics I think.
> But I have a real mini2440 and I am positively sure that WP
> is active high. CD is active low, yes.
> 
> Do you know someone that you trust that could confirm this?
> 
> > 
> > This is really an old code so I am just quite surprised that it was not
> > reported before. Not able to write to SD card (for example if it is
> > rootfs) should be spotted quite early.
> 
> I don't think anyone tried a recent kernel, that's why.
> And the mini2440 has been kind of replaced by the mini6410,
> I'm not sure it's still in production. Apart from me, I
> don't think anyone still uses it. If someone does, I
> heavily doubt that person will try to boot a 4.something
> kernel on it.
> 
> In the 2.6.32.63 kernel it's all different.
> 
> We have s3cmci_get_ro in drivers/mmc/host/s3cmci.c
> that calls s3c2410_gpio_getpin in arch/arm/plat-s3c24xx/gpio.c
> that returns the WP bit as is read from the GPIO.
> s3cmci_get_ro will return > 0 if the bit is set and
> wprotect_invert is not set. For mini2440, wprotect_invert
> is not set (actually it does not seem to be set anywhere
> in the kernel tree, is it used at all in 2.6.32.63?). So
> it's returned as is. Getting 1 from GPIO means Read Only.
> 
> Then we have s3cmci_card_present, also in drivers/mmc/host/s3cmci.c,
> that reads the CD bit from the GPIO, but take the opposite value
> and then returns the opposite of the result if detect_invert
> is 1. For mini2440 it's not 1, but 0. So we return the opposite
> of the CD bit read from the GPIO, which means active low.
> 
> I'm not an electronic professional so I don't know how to interpret
> the schematics. My experiment with my mini2440 says that:
> - no card:         WP bit = 1, CD bit = 1
> - card read/write: WP bit = 0, CD bit = 0
> - card read only:  WP bit = 1, CD bit = 0
> By "WP bit" I mean the value read from GPH8.
> By "CD bit" I mean the value read from GPG8.
> 
> So I don't know what to do. If you don't trust me and you know
> no one that you trust that would confirm my findings, then it's
> game over.
> 
> I can do things that you ask me to do to prove my claims.
> 
> I can provide a simple userland program to be run on a mini2440
> that demonstrates this as well (open /dev/mem, mmap 0x56000000,
> reads GPG and GPH and prints the values).

You provided really good explanation so let's go with your patch.

Thanks, applied.

Best regards,
Krzysztof