[PATCH] mini2440 MMC correct write protect detection

[krzk@kernel.org (Krzysztof Kozlowski)]

On Thu, Sep 06, 2018 at 05:53:39PM +0200, Krzysztof Kozlowski wrote:
> 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.

... and dropped. Checkpatch fails:
https://krzk.eu/#/builders/26/builds/121

Please fix checkpatch errors and resubmit with proper patch style and
adjusted title: "ARM: s3c24xx: Correct SD card write protect detection
on Mini2440".


Best regards,
Krzysztof