[2/2] serial: mctrl_gpio: Support all GPIO suffixes (gpios vs gpio)
diff mbox series

Message ID 20190808132543.26274-2-sr@denx.de
State New
Headers show
Series
  • [1/2] gpiolib: Add for_each_gpio_suffix() helper
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Commit Message

Stefan Roese Aug. 8, 2019, 1:25 p.m. UTC
This patch fixes a backward compatibility issue, when boards use the
old style GPIO suffix "-gpio" instead of the new "-gpios". This
potential problem has been introduced by commit d99482673f95 ("serial:
mctrl_gpio: Check if GPIO property exisits before requesting it").

This patch now fixes this issue by iterating over all supported GPIO
suffixes by using the newly introduced for_each_gpio_suffix() helper.

Also, the string buffer is now allocated on the stack to avoid the
problem of allocation in a loop and its potential failure.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Pavel Machek <pavel@denx.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/serial_mctrl_gpio.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

Comments

Andy Shevchenko Aug. 8, 2019, 1:48 p.m. UTC | #1
On Thu, Aug 08, 2019 at 03:25:43PM +0200, Stefan Roese wrote:
> This patch fixes a backward compatibility issue, when boards use the
> old style GPIO suffix "-gpio" instead of the new "-gpios". This
> potential problem has been introduced by commit d99482673f95 ("serial:
> mctrl_gpio: Check if GPIO property exisits before requesting it").
> 
> This patch now fixes this issue by iterating over all supported GPIO
> suffixes by using the newly introduced for_each_gpio_suffix() helper.
> 
> Also, the string buffer is now allocated on the stack to avoid the
> problem of allocation in a loop and its potential failure.

>  	for (i = 0; i < UART_GPIO_MAX; i++) {
>  		enum gpiod_flags flags;
> -		char *gpio_str;
> +		const char *suffix;
> +		char gpio_str[32];	/* 32 is max size of property name */

Hmm... don't we have some define for the maximum length of property?

Or maybe we can still continue using kasprintf() approach?

>  		bool present;
> +		int k;
> +
> +		/*
> +		 * Check if GPIO property exists and continue if not. Iterate
> +		 * over all supported GPIO suffixes (foo-gpios vs. foo-gpio).
> +		 */
> +		for_each_gpio_suffix(k, suffix) {
> +			snprintf(gpio_str, sizeof(gpio_str), "%s-%s",
> +				 mctrl_gpios_desc[i].name, suffix);
> +
> +			present = device_property_present(dev, gpio_str);
> +			if (present)
> +				break;
> +		}
>  
> -		/* Check if GPIO property exists and continue if not */
> -		gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
> -				     mctrl_gpios_desc[i].name);
> -		if (!gpio_str)
> -			continue;
> -

> -		present = device_property_present(dev, gpio_str);

Because there is no more explicit assignment of present outside of the loop,
the compiler may warn about uninitialized variable in use...

> -		kfree(gpio_str);

>  		if (!present)

...here.

>  			continue;
Stefan Roese Aug. 8, 2019, 1:59 p.m. UTC | #2
Hi Andy,

On 08.08.19 15:48, Andy Shevchenko wrote:
> On Thu, Aug 08, 2019 at 03:25:43PM +0200, Stefan Roese wrote:
>> This patch fixes a backward compatibility issue, when boards use the
>> old style GPIO suffix "-gpio" instead of the new "-gpios". This
>> potential problem has been introduced by commit d99482673f95 ("serial:
>> mctrl_gpio: Check if GPIO property exisits before requesting it").
>>
>> This patch now fixes this issue by iterating over all supported GPIO
>> suffixes by using the newly introduced for_each_gpio_suffix() helper.
>>
>> Also, the string buffer is now allocated on the stack to avoid the
>> problem of allocation in a loop and its potential failure.
> 
>>   	for (i = 0; i < UART_GPIO_MAX; i++) {
>>   		enum gpiod_flags flags;
>> -		char *gpio_str;
>> +		const char *suffix;
>> +		char gpio_str[32];	/* 32 is max size of property name */
> 
> Hmm... don't we have some define for the maximum length of property?

I've come up with this assumption from this code (identical comment):

https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib-of.c#L293

(and other places in drivers/gpio/*)
  
> Or maybe we can still continue using kasprintf() approach?

Frankly, I was feeling a bit uncomfortable with this memory allocation
in a loop. And Pavel also commented on this:

https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2066286.html

So I would really prefer to move this buffer to the stack instead.
  
>>   		bool present;
>> +		int k;
>> +
>> +		/*
>> +		 * Check if GPIO property exists and continue if not. Iterate
>> +		 * over all supported GPIO suffixes (foo-gpios vs. foo-gpio).
>> +		 */
>> +		for_each_gpio_suffix(k, suffix) {
>> +			snprintf(gpio_str, sizeof(gpio_str), "%s-%s",
>> +				 mctrl_gpios_desc[i].name, suffix);
>> +
>> +			present = device_property_present(dev, gpio_str);
>> +			if (present)
>> +				break;
>> +		}
>>   
>> -		/* Check if GPIO property exists and continue if not */
>> -		gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
>> -				     mctrl_gpios_desc[i].name);
>> -		if (!gpio_str)
>> -			continue;
>> -
> 
>> -		present = device_property_present(dev, gpio_str);
> 
> Because there is no more explicit assignment of present outside of the loop,
> the compiler may warn about uninitialized variable in use...
> 
>> -		kfree(gpio_str);
> 
>>   		if (!present)
> 
> ...here.

My compiler does not warn (MIPS GCC 8.1) but I see your point. I'll add
an initialization in the next version.

Thanks,
Stefan
Andy Shevchenko Aug. 12, 2019, 10:53 a.m. UTC | #3
On Thu, Aug 08, 2019 at 03:59:36PM +0200, Stefan Roese wrote:
> On 08.08.19 15:48, Andy Shevchenko wrote:
> > On Thu, Aug 08, 2019 at 03:25:43PM +0200, Stefan Roese wrote:
> > > This patch fixes a backward compatibility issue, when boards use the
> > > old style GPIO suffix "-gpio" instead of the new "-gpios". This
> > > potential problem has been introduced by commit d99482673f95 ("serial:
> > > mctrl_gpio: Check if GPIO property exisits before requesting it").
> > > 
> > > This patch now fixes this issue by iterating over all supported GPIO
> > > suffixes by using the newly introduced for_each_gpio_suffix() helper.
> > > 
> > > Also, the string buffer is now allocated on the stack to avoid the
> > > problem of allocation in a loop and its potential failure.
> > 
> > >   	for (i = 0; i < UART_GPIO_MAX; i++) {
> > >   		enum gpiod_flags flags;
> > > -		char *gpio_str;
> > > +		const char *suffix;
> > > +		char gpio_str[32];	/* 32 is max size of property name */
> > 
> > Hmm... don't we have some define for the maximum length of property?
> 
> I've come up with this assumption from this code (identical comment):
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib-of.c#L293
> 
> (and other places in drivers/gpio/*)

I tried hard to find an evidence of this in Linux kernel, I assume that comes
from DT compiler or something, but fail. Linux kernel OF properties handling is
written in the assumption of arbitrary length of the property name.

It might be that my hard was not hard at all and I missed something.

> > Or maybe we can still continue using kasprintf() approach?
> 
> Frankly, I was feeling a bit uncomfortable with this memory allocation
> in a loop. And Pavel also commented on this:
> 
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2066286.html

If memory allocator fails, it's a big issue, and what will happen next probably
much less important.

> So I would really prefer to move this buffer to the stack instead.
Geert Uytterhoeven Aug. 12, 2019, 11:17 a.m. UTC | #4
Hi Stefan,

On Thu, Aug 8, 2019 at 3:25 PM Stefan Roese <sr@denx.de> wrote:
> This patch fixes a backward compatibility issue, when boards use the
> old style GPIO suffix "-gpio" instead of the new "-gpios". This
> potential problem has been introduced by commit d99482673f95 ("serial:
> mctrl_gpio: Check if GPIO property exisits before requesting it").
>
> This patch now fixes this issue by iterating over all supported GPIO
> suffixes by using the newly introduced for_each_gpio_suffix() helper.
>
> Also, the string buffer is now allocated on the stack to avoid the
> problem of allocation in a loop and its potential failure.
>
> Signed-off-by: Stefan Roese <sr@denx.de>

Do we really need to spread this *-gpio" legacy support all over the kernel?

Seeing the only in-kernel users of legacy "rts-gpio" are

    arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio0 13
GPIO_ACTIVE_HIGH>;
    arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio2 15
GPIO_ACTIVE_HIGH>;
    arch/arm/boot/dts/am335x-pdu001.dts:    rts-gpio = <&gpio1 9
GPIO_ACTIVE_HIGH>;

and this is handled by omap-serial.c, predating mctrl_gpio, I'd like to
reconsider.

Documentation/devicetree/bindings/serial/serial.txt always described
the "*-gpios"
variants, so there should be no users of the legacy "*-gpio" variants.

Gr{oetje,eeting}s,

                        Geert
Stefan Roese Aug. 12, 2019, 11:53 a.m. UTC | #5
Hi Geert,

On 12.08.19 13:17, Geert Uytterhoeven wrote:
> Hi Stefan,
> 
> On Thu, Aug 8, 2019 at 3:25 PM Stefan Roese <sr@denx.de> wrote:
>> This patch fixes a backward compatibility issue, when boards use the
>> old style GPIO suffix "-gpio" instead of the new "-gpios". This
>> potential problem has been introduced by commit d99482673f95 ("serial:
>> mctrl_gpio: Check if GPIO property exisits before requesting it").
>>
>> This patch now fixes this issue by iterating over all supported GPIO
>> suffixes by using the newly introduced for_each_gpio_suffix() helper.
>>
>> Also, the string buffer is now allocated on the stack to avoid the
>> problem of allocation in a loop and its potential failure.
>>
>> Signed-off-by: Stefan Roese <sr@denx.de>
> 
> Do we really need to spread this *-gpio" legacy support all over the kernel?
> 
> Seeing the only in-kernel users of legacy "rts-gpio" are
> 
>      arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio0 13
> GPIO_ACTIVE_HIGH>;
>      arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio2 15
> GPIO_ACTIVE_HIGH>;
>      arch/arm/boot/dts/am335x-pdu001.dts:    rts-gpio = <&gpio1 9
> GPIO_ACTIVE_HIGH>;
> 
> and this is handled by omap-serial.c, predating mctrl_gpio, I'd like to
> reconsider.
> 
> Documentation/devicetree/bindings/serial/serial.txt always described
> the "*-gpios"
> variants, so there should be no users of the legacy "*-gpio" variants.

Hmmm, you were the one to comment about supporting (not breaking) the
"-gpio" variant:

https://lkml.org/lkml/2019/6/24/248

That was my main motivation to work on this patch.

If we all agree, that only the documented "-gpios" variant needs to
be supported, then we can drop this patch.

Thanks,
Stefan
Geert Uytterhoeven Aug. 12, 2019, 12:11 p.m. UTC | #6
Hi Stefan,

On Mon, Aug 12, 2019 at 1:54 PM Stefan Roese <sr@denx.de> wrote:
> On 12.08.19 13:17, Geert Uytterhoeven wrote:
> > On Thu, Aug 8, 2019 at 3:25 PM Stefan Roese <sr@denx.de> wrote:
> >> This patch fixes a backward compatibility issue, when boards use the
> >> old style GPIO suffix "-gpio" instead of the new "-gpios". This
> >> potential problem has been introduced by commit d99482673f95 ("serial:
> >> mctrl_gpio: Check if GPIO property exisits before requesting it").
> >>
> >> This patch now fixes this issue by iterating over all supported GPIO
> >> suffixes by using the newly introduced for_each_gpio_suffix() helper.
> >>
> >> Also, the string buffer is now allocated on the stack to avoid the
> >> problem of allocation in a loop and its potential failure.
> >>
> >> Signed-off-by: Stefan Roese <sr@denx.de>
> >
> > Do we really need to spread this *-gpio" legacy support all over the kernel?
> >
> > Seeing the only in-kernel users of legacy "rts-gpio" are
> >
> >      arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio0 13
> > GPIO_ACTIVE_HIGH>;
> >      arch/arm/boot/dts/am335x-nano.dts:      rts-gpio = <&gpio2 15
> > GPIO_ACTIVE_HIGH>;
> >      arch/arm/boot/dts/am335x-pdu001.dts:    rts-gpio = <&gpio1 9
> > GPIO_ACTIVE_HIGH>;
> >
> > and this is handled by omap-serial.c, predating mctrl_gpio, I'd like to
> > reconsider.
> >
> > Documentation/devicetree/bindings/serial/serial.txt always described
> > the "*-gpios"
> > variants, so there should be no users of the legacy "*-gpio" variants.
>
> Hmmm, you were the one to comment about supporting (not breaking) the
> "-gpio" variant:
>
> https://lkml.org/lkml/2019/6/24/248
>
> That was my main motivation to work on this patch.

I know. That's why I wrote "reconsider".  Before, I assumed there were actual
users of the legacy properties, which turned out to be wrong.

IMHO no driver should be aware there can be multiple possible suffixes.

Sorry for the trouble.

> If we all agree, that only the documented "-gpios" variant needs to
> be supported, then we can drop this patch.

BTW, I'm still wondering if d99482673f950817 ("serial: mctrl_gpio: Check
if GPIO property exisits before requesting it") is the right fix.
This is a place where we rely explicitly on named GPIOs being present, so
IMHO the ACPI code should not return a random GPIO instead.

Gr{oetje,eeting}s,

                        Geert
Andy Shevchenko Aug. 12, 2019, 12:31 p.m. UTC | #7
On Mon, Aug 12, 2019 at 02:11:42PM +0200, Geert Uytterhoeven wrote:
> On Mon, Aug 12, 2019 at 1:54 PM Stefan Roese <sr@denx.de> wrote:
> > On 12.08.19 13:17, Geert Uytterhoeven wrote:

> > If we all agree, that only the documented "-gpios" variant needs to
> > be supported, then we can drop this patch.
> 
> BTW, I'm still wondering if d99482673f950817 ("serial: mctrl_gpio: Check
> if GPIO property exisits before requesting it") is the right fix.
> This is a place where we rely explicitly on named GPIOs being present, so
> IMHO the ACPI code should not return a random GPIO instead.

ACPI is not taking it to consideration for now. That is, there is no support of
mctrl gpio for ACPI.
Pavel Machek Aug. 13, 2019, 11:42 a.m. UTC | #8
On Mon 2019-08-12 13:53:07, Andy Shevchenko wrote:
> On Thu, Aug 08, 2019 at 03:59:36PM +0200, Stefan Roese wrote:
> > On 08.08.19 15:48, Andy Shevchenko wrote:
> > > On Thu, Aug 08, 2019 at 03:25:43PM +0200, Stefan Roese wrote:
> > > > This patch fixes a backward compatibility issue, when boards use the
> > > > old style GPIO suffix "-gpio" instead of the new "-gpios". This
> > > > potential problem has been introduced by commit d99482673f95 ("serial:
> > > > mctrl_gpio: Check if GPIO property exisits before requesting it").
> > > > 
> > > > This patch now fixes this issue by iterating over all supported GPIO
> > > > suffixes by using the newly introduced for_each_gpio_suffix() helper.
> > > > 
> > > > Also, the string buffer is now allocated on the stack to avoid the
> > > > problem of allocation in a loop and its potential failure.
> > > 
> > > >   	for (i = 0; i < UART_GPIO_MAX; i++) {
> > > >   		enum gpiod_flags flags;
> > > > -		char *gpio_str;
> > > > +		const char *suffix;
> > > > +		char gpio_str[32];	/* 32 is max size of property name */
> > > 
> > > Hmm... don't we have some define for the maximum length of property?
> > 
> > I've come up with this assumption from this code (identical comment):
> > 
> > https://elixir.bootlin.com/linux/latest/source/drivers/gpio/gpiolib-of.c#L293
> > 
> > (and other places in drivers/gpio/*)
> 
> I tried hard to find an evidence of this in Linux kernel, I assume that comes
> from DT compiler or something, but fail. Linux kernel OF properties handling is
> written in the assumption of arbitrary length of the property name.
> 
> It might be that my hard was not hard at all and I missed something.
> 
> > > Or maybe we can still continue using kasprintf() approach?
> > 
> > Frankly, I was feeling a bit uncomfortable with this memory allocation
> > in a loop. And Pavel also commented on this:
> > 
> > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2066286.html
> 
> If memory allocator fails, it's a big issue, and what will happen next probably
> much less important.

Not... really. With "too big" allocations, it will fail.

Anyway, my point is that allocating in a loop for this is slow and
ugly. If we don't have a maximum property length, we should probably
invent some. I mean, we can agree that 64KB property name is not okay,
right?


								Pavel
Andy Shevchenko Aug. 13, 2019, 12:15 p.m. UTC | #9
On Tue, Aug 13, 2019 at 01:42:58PM +0200, Pavel Machek wrote:
> On Mon 2019-08-12 13:53:07, Andy Shevchenko wrote:
> > On Thu, Aug 08, 2019 at 03:59:36PM +0200, Stefan Roese wrote:
> > > On 08.08.19 15:48, Andy Shevchenko wrote:
> > > > On Thu, Aug 08, 2019 at 03:25:43PM +0200, Stefan Roese wrote:

> > I tried hard to find an evidence of this in Linux kernel, I assume that comes
> > from DT compiler or something, but fail. Linux kernel OF properties handling is
> > written in the assumption of arbitrary length of the property name.
> > 
> > It might be that my hard was not hard at all and I missed something.
> > 
> > > > Or maybe we can still continue using kasprintf() approach?
> > > 
> > > Frankly, I was feeling a bit uncomfortable with this memory allocation
> > > in a loop. And Pavel also commented on this:
> > > 
> > > https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2066286.html
> > 
> > If memory allocator fails, it's a big issue, and what will happen next probably
> > much less important.
> 
> Not... really. With "too big" allocations, it will fail.

Yeah, or with relatively small if memory is too much fragmented.
But we are talking about really small allocations here in most cases, right?

> Anyway, my point is that allocating in a loop for this is slow and
> ugly. If we don't have a maximum property length, we should probably
> invent some. I mean, we can agree that 64KB property name is not okay,
> right?

My point that is should be declared on the level of property API.
Restricting it on the level of one, 'client' to that API, framework is not
a solution.

Patch
diff mbox series

diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
index 2b400189be91..d444fdaa280a 100644
--- a/drivers/tty/serial/serial_mctrl_gpio.c
+++ b/drivers/tty/serial/serial_mctrl_gpio.c
@@ -15,6 +15,7 @@ 
 #include <linux/property.h>
 
 #include "serial_mctrl_gpio.h"
+#include "../../gpio/gpiolib.h"
 
 struct mctrl_gpios {
 	struct uart_port *port;
@@ -117,17 +118,24 @@  struct mctrl_gpios *mctrl_gpio_init_noauto(struct device *dev, unsigned int idx)
 
 	for (i = 0; i < UART_GPIO_MAX; i++) {
 		enum gpiod_flags flags;
-		char *gpio_str;
+		const char *suffix;
+		char gpio_str[32];	/* 32 is max size of property name */
 		bool present;
+		int k;
+
+		/*
+		 * Check if GPIO property exists and continue if not. Iterate
+		 * over all supported GPIO suffixes (foo-gpios vs. foo-gpio).
+		 */
+		for_each_gpio_suffix(k, suffix) {
+			snprintf(gpio_str, sizeof(gpio_str), "%s-%s",
+				 mctrl_gpios_desc[i].name, suffix);
+
+			present = device_property_present(dev, gpio_str);
+			if (present)
+				break;
+		}
 
-		/* Check if GPIO property exists and continue if not */
-		gpio_str = kasprintf(GFP_KERNEL, "%s-gpios",
-				     mctrl_gpios_desc[i].name);
-		if (!gpio_str)
-			continue;
-
-		present = device_property_present(dev, gpio_str);
-		kfree(gpio_str);
 		if (!present)
 			continue;