[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Vincent Stehlé]

Add a detection at runtime of the boot from USB on i.MX6, and invalidate
the D-cache only in that case.

The USB boot detection method is taken from Freescale u-boot commit
1309b1ed78b3 ("ENGR00315499-8 Auto check if boot from usb").

This repairs u-boot when it is built with CONFIG_SKIP_LOWLEVEL_INIT
defined, and is booted from another u-boot, which booted from SD card,
for example.

Signed-off-by: Vincent Stehl? <vincent.stehle@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Frank Li <Frank.li@freescale.com>
Cc: Nitin Garg <nitin.garg@freescale.com>
---
 arch/arm/cpu/armv7/mx6/soc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm/cpu/armv7/mx6/soc.c b/arch/arm/cpu/armv7/mx6/soc.c
index 21ef9d0..774f078 100644
--- a/arch/arm/cpu/armv7/mx6/soc.c
+++ b/arch/arm/cpu/armv7/mx6/soc.c
@@ -350,6 +350,18 @@ int board_postclk_init(void)
 	return 0;
 }
 
+/*
+ * Determine if we booted from USB.
+ *
+ * We look at the USBPH0_PWD0.RXPWDRX register to determine if the USB
+ * PHY is powered on or off. If the USB PHY is turned on, we assume that
+ * the ROM booted us from USB.
+ */
+static bool is_boot_from_usb(void)
+{
+	return !(readl(USB_PHY0_BASE_ADDR) & (1<<20));
+}
+
 #ifndef CONFIG_SYS_DCACHE_OFF
 void enable_caches(void)
 {
@@ -360,7 +372,8 @@ void enable_caches(void)
 #endif
 
 	/* Avoid random hang when download by usb */
-	invalidate_dcache_all();
+	if (is_boot_from_usb())
+		invalidate_dcache_all();
 
 	/* Enable D-cache. I-cache is already enabled in start.S */
 	dcache_enable();
-- 
2.1.4

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Li Frank]

> From: Vincent Stehl? [mailto:vincent.stehle at freescale.com]
> Sent: Friday, May 22, 2015 9:53 AM
> To: u-boot at lists.denx.de
> Cc: Stehle Vincent-B46079; Stefano Babic; Estevam Fabio-R49496; Li Frank-
> B20596; Garg Nitin-B37173
> Subject: [PATCH] mx6: invalidate D-cache only when booting from USB
> 
> Add a detection at runtime of the boot from USB on i.MX6, and invalidate the
> D-cache only in that case.
> 
> The USB boot detection method is taken from Freescale u-boot commit
> 1309b1ed78b3 ("ENGR00315499-8 Auto check if boot from usb").
> 
> This repairs u-boot when it is built with CONFIG_SKIP_LOWLEVEL_INIT
> defined, and is booted from another u-boot, which booted from SD card, for
> example.
> 
> Signed-off-by: Vincent Stehl? <vincent.stehle@freescale.com>
> Cc: Stefano Babic <sbabic@denx.de>
> Cc: Fabio Estevam <fabio.estevam@freescale.com>
> Cc: Frank Li <Frank.li@freescale.com>
> Cc: Nitin Garg <nitin.garg@freescale.com>
> ---
>  arch/arm/cpu/armv7/mx6/soc.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/cpu/armv7/mx6/soc.c
> b/arch/arm/cpu/armv7/mx6/soc.c index 21ef9d0..774f078 100644
> --- a/arch/arm/cpu/armv7/mx6/soc.c
> +++ b/arch/arm/cpu/armv7/mx6/soc.c
> @@ -350,6 +350,18 @@ int board_postclk_init(void)
>  	return 0;
>  }
> 
> +/*
> + * Determine if we booted from USB.
> + *
> + * We look at the USBPH0_PWD0.RXPWDRX register to determine if the
> USB
> + * PHY is powered on or off. If the USB PHY is turned on, we assume
> +that
> + * the ROM booted us from USB.
> + */
> +static bool is_boot_from_usb(void)
> +{
> +	return !(readl(USB_PHY0_BASE_ADDR) & (1<<20)); }
> +
>  #ifndef CONFIG_SYS_DCACHE_OFF
>  void enable_caches(void)
>  {
> @@ -360,7 +372,8 @@ void enable_caches(void)  #endif
> 
>  	/* Avoid random hang when download by usb */
> -	invalidate_dcache_all();
> +	if (is_boot_from_usb())
> +		invalidate_dcache_all();

How about second uboot save in usb mass storage device?

Best regards
Frank Li

> 
>  	/* Enable D-cache. I-cache is already enabled in start.S */
>  	dcache_enable();
> --
> 2.1.4

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Vincent Stehlé]

On 05/22/2015 05:15 PM, Li Frank-B20596 wrote:
..
> How about second uboot save in usb mass storage device?

Hi Frank,

I cannot test but I guess this will behave the same as without the
patch, which means that it will probably not boot.

Granted, the detection method in is_boot_from_usb() is an approximation,
but it repairs one case already and should not break anything.

Best regards,

V.

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Stefano Babic]

Hi Vincent,

On 22/05/2015 16:52, Vincent Stehl? wrote:
> Add a detection at runtime of the boot from USB on i.MX6, and invalidate
> the D-cache only in that case.
> 
> The USB boot detection method is taken from Freescale u-boot commit
> 1309b1ed78b3 ("ENGR00315499-8 Auto check if boot from usb").
> 
> This repairs u-boot when it is built with CONFIG_SKIP_LOWLEVEL_INIT
> defined, and is booted from another u-boot, which booted from SD card,
> for example.

Please help me to find the use case. I searched in all i.MX6 boards in
mainline, but none of them is setting CONFIG_SKIP_LOWLEVEL_INIT. Can you
tell me on which board there is this issue ?

> 
> Signed-off-by: Vincent Stehl? <vincent.stehle@freescale.com>
> Cc: Stefano Babic <sbabic@denx.de>
> Cc: Fabio Estevam <fabio.estevam@freescale.com>
> Cc: Frank Li <Frank.li@freescale.com>
> Cc: Nitin Garg <nitin.garg@freescale.com>
> ---
>  arch/arm/cpu/armv7/mx6/soc.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/cpu/armv7/mx6/soc.c b/arch/arm/cpu/armv7/mx6/soc.c
> index 21ef9d0..774f078 100644
> --- a/arch/arm/cpu/armv7/mx6/soc.c
> +++ b/arch/arm/cpu/armv7/mx6/soc.c
> @@ -350,6 +350,18 @@ int board_postclk_init(void)
>  	return 0;
>  }
>  
> +/*
> + * Determine if we booted from USB.
> + *
> + * We look at the USBPH0_PWD0.RXPWDRX register to determine if the USB
> + * PHY is powered on or off. If the USB PHY is turned on, we assume that
> + * the ROM booted us from USB.
> + */
> +static bool is_boot_from_usb(void)
> +{
> +	return !(readl(USB_PHY0_BASE_ADDR) & (1<<20));
> +}

This looks like a hack. I understand this can work in your case, but can
we set as general case ? You check power for PHY0, but what about if a
board is using PHY1 ?

Anyway, is it not possible to get the boot storage from the SRC ?

> +
>  #ifndef CONFIG_SYS_DCACHE_OFF
>  void enable_caches(void)
>  {
> @@ -360,7 +372,8 @@ void enable_caches(void)
>  #endif
>  
>  	/* Avoid random hang when download by usb */
> -	invalidate_dcache_all();
> +	if (is_boot_from_usb())
> +		invalidate_dcache_all();

I cannot understand well this. The correct implementation seems correct
to me. And if you have issues booting with USB, why are you changing the
behavior in all other cases *except* booting from USB, where you rely on
the current implementation invalidating the cache ?

Best regards,
Stefano Babic

-- 
=====================================================================
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: sbabic at denx.de
=====================================================================

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Vincent]

Stefano wrote:
> Please help me to find the use case. I searched in all i.MX6 boards in
> mainline, but none of them is setting CONFIG_SKIP_LOWLEVEL_INIT. Can you
> tell me on which board there is this issue ?

Hi Stefano,

Thank you for taking the time to look at this proposed patch.

You are right, this is a "non standard" use case. What I am trying to do
is to boot u-boot with u-boot on i.MX6Q Sabre SD :)

Here are more details on what I would like to do:

1. Boot "old" u-boot from SD card.
2. "old" u-boot loads "new" u-boot from network with 'dhcp' command.
3. "old" u-boot boots "new" u-boot with 'go' command.

This is not so easy to achieve, it seems. I learned that in this
peculiar use case it is necessary to set CONFIG_SKIP_LOWLEVEL_INIT when
building the "new" u-boot, as hinted by the README.

Also I found out that the call to invalidate_dcache_all() would prevent
the boot for the aforementioned use case. "protecting" the call (as done
in Freescale u-boot) "repairs" my use case, and I verified that it does
not alter the boot through USB.

(boot from USB detection code)
> This looks like a hack. I understand this can work in your case, but can
> we set as general case ? You check power for PHY0, but what about if a
> board is using PHY1 ?
> Anyway, is it not possible to get the boot storage from the SRC ?

You are right, the detection code is not perfect. This is the one I
borrowed from Freescale u-boot, though, so it is reasonably tested "in
the field".

About the phy0/phy1 distinction, I think we can boot only from OTG PHY0
so no worry.

About the SRC; I am not sure you can get the desired information from
there, as booting from USB is a ROM "fallback".

(adding a condition to cache invalidation)
> I cannot understand well this. The correct implementation seems correct
> to me. And if you have issues booting with USB, why are you changing the
> behavior in all other cases *except* booting from USB, where you rely on
> the current implementation invalidating the cache ?

In my case, it is NOT booting with USB rather, it is booting from
another u-boot. I discovered that invalidating the caches in this case
breaks the boot.

The current implementation invalidates the cache in all cases for i.MX6,
as it believes it is always booting from the ROM.

As the comments hint that invalidating the caches is necessary only when
booting from USB (from ROM), I tried to restrict a bit more the
invalidation to this "boot from USB" case. The detection is not perfect,
but it is enough to repair my use case, at least.

Best regards,

V.

[U-Boot] [PATCH] mx6: invalidate D-cache only when booting from USB

[Stefano Babic]

Hi Vincent,

On 26/05/2015 17:16, Vincent wrote:
> Stefano wrote:
>> Please help me to find the use case. I searched in all i.MX6 boards in
>> mainline, but none of them is setting CONFIG_SKIP_LOWLEVEL_INIT. Can you
>> tell me on which board there is this issue ?
> 
> Hi Stefano,
> 
> Thank you for taking the time to look at this proposed patch.
> 
> You are right, this is a "non standard" use case. What I am trying to do
> is to boot u-boot with u-boot on i.MX6Q Sabre SD :)

ok - so there is a chain of u-boot, and the last one loads and starts
the kernel.

> 
> Here are more details on what I would like to do:
> 
> 1. Boot "old" u-boot from SD card.
> 2. "old" u-boot loads "new" u-boot from network with 'dhcp' command.
> 3. "old" u-boot boots "new" u-boot with 'go' command.

ok, understood what you are doing.

> This is not so easy to achieve, it seems. I learned that in this
> peculiar use case it is necessary to set CONFIG_SKIP_LOWLEVEL_INIT when
> building the "new" u-boot, as hinted by the README.

This use case can happen and I had in the past, but I confess with other
SOCs. It can be requested if U-Boot in field is outdated and a new
U-Boot is required, but updating U-Boot is dangerous, and a chain of
multiple (two) U-Boot is chosen.

Anyway, to reach the goal, you have to check the initialization
routines. CONFIG_SKIP_LOWLEVEL_INIT should ensure that the DDR
controller is not initialized twice. On imx, I guess you will have a
u-boot.imx on the board, while the "new" u-boot is in "bin" format. In
fact, you do not nned the DCD table that is parsed and applied only by
the SOC's Boot ROM.

> 
> Also I found out that the call to invalidate_dcache_all() would prevent
> the boot for the aforementioned use case. "protecting" the call (as done
> in Freescale u-boot) "repairs" my use case, and I verified that it does
> not alter the boot through USB.

Before booting the kernel, U-Boot calls "cleanup_before_linux()" to let
the SOC in a well knon state. Cache are disable at this point, and this
let the kernel doing evething with the hardware.
However, when you load U-Boot as different image, this cleanup is not
called at all. Maybe it works in your case if cleanup is called even by
loading your second u-boot and not only by starting Linux.

> 
> (boot from USB detection code)
>> This looks like a hack. I understand this can work in your case, but can
>> we set as general case ? You check power for PHY0, but what about if a
>> board is using PHY1 ?
>> Anyway, is it not possible to get the boot storage from the SRC ?
> 
> You are right, the detection code is not perfect. This is the one I
> borrowed from Freescale u-boot, though, so it is reasonably tested "in
> the field".

This cannot be generalized - maybe it does not work on all boards, even
if in your case it does the job.

> 
> About the phy0/phy1 distinction, I think we can boot only from OTG PHY0
> so no worry.
> 
> About the SRC; I am not sure you can get the desired information from
> there, as booting from USB is a ROM "fallback".
> 
> (adding a condition to cache invalidation)
>> I cannot understand well this. The correct implementation seems correct
>> to me. And if you have issues booting with USB, why are you changing the
>> behavior in all other cases *except* booting from USB, where you rely on
>> the current implementation invalidating the cache ?
> 
> In my case, it is NOT booting with USB rather, it is booting from
> another u-boot. I discovered that invalidating the caches in this case
> breaks the boot.

It should not be. And the second U-Boot should not be started with
enabled cache, as it is done now.

> 
> The current implementation invalidates the cache in all cases for i.MX6,
> as it believes it is always booting from the ROM.
> 
> As the comments hint that invalidating the caches is necessary only when
> booting from USB (from ROM), I tried to restrict a bit more the
> invalidation to this "boot from USB" case. The detection is not perfect,
> but it is enough to repair my use case, at least.
> 

Best regards,
Stefano Babic



-- 
=====================================================================
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-53 Fax: +49-8142-66989-80 Email: sbabic at denx.de
=====================================================================