[PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Vishwanath BS]

This patch adds comments on precatution to be taken if Global Warm reset is
used as the means to trigger sysem reset.

Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
Cc: Paul Walmsley <paul@pwsan.com>
---
 arch/arm/mach-omap2/prcm.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mach-omap2/prcm.c b/arch/arm/mach-omap2/prcm.c
index c201374..e37639c
--- a/arch/arm/mach-omap2/prcm.c
+++ b/arch/arm/mach-omap2/prcm.c
@@ -157,6 +157,34 @@ void omap_prcm_arch_reset(char mode, const char *cmd)
 	else
 		WARN_ON(1);
 
+	/*
+	 * As per Errata i520, In some cases, user will not be able to
+	 * access DDR memory after warm-reset.
+	 * This situation occurs while the warm-reset happens during a read
+	 * access to DDR memory. In that particular condition, DDR memory
+	 * does not respond to a corrupted read command due to the warm
+	 * reset occurence but SDRC is waiting for read completion.
+	 * SDRC is not sensitive to the warm reset, but the interconect is
+	 * reset on the fly, thus causing a misalignment between SDRC logic,
+	 * interconect logic and DDR memory state.
+	 * WORKAROUND:
+	 * Steps to perform before a Warm reset is trigged:
+	 * 1. enable self-refresh on idle request
+	 * 2. put SDRC in idle
+	 * 3. wait until SDRC goes to idle
+	 * 4. generate SW reset (Global SW reset)
+	 *
+	 * Steps to be performed after warm reset occurs (in bootloader):
+	 * if HW warm reset is the source, apply below steps before any
+	 * accesses to SDRAM:
+	 * 1. Reset SMS and SDRC and wait till reset is complete
+	 * 2. Re-initialize SMS, SDRC and memory
+	 *
+	 * NOTE: Above work around is required only if arch reset is implemented
+	 * using Global SW reset(GLOBAL_SW_RST). DPLL3 reset does not need
+	 * the WA since it resets SDRC as well as part of cold reset.
+	 */
+
 	if (cpu_is_omap24xx() || cpu_is_omap34xx())
 		prm_set_mod_reg_bits(OMAP_RST_DPLL3_MASK, prcm_offs,
 						 OMAP2_RM_RSTCTRL);
-- 
1.7.0.4

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Premi, Sanjeev]

> -----Original Message-----
> From: linux-omap-owner@vger.kernel.org 
> [mailto:linux-omap-owner@vger.kernel.org] On Behalf Of 
> Sripathy, Vishwanath
> Sent: Tuesday, October 05, 2010 7:36 PM
> To: linux-omap@vger.kernel.org
> Cc: Sripathy, Vishwanath; Paul Walmsley
> Subject: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 
> for Global SW reset
> 
> This patch adds comments on precatution to be taken if Global 

s/precatution /precaution/ ?

[snip]..[snip]

Re: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Paul Walmsley]

On Tue, 5 Oct 2010, Vishwanath BS wrote:

> This patch adds comments on precatution to be taken if Global Warm reset is
> used as the means to trigger sysem reset.
> 
> Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
> Cc: Paul Walmsley <paul@pwsan.com>

Thanks, queued for 2.6.38 with Sanjeev's spelling fix.


- Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Vishwanath Sripathy]

Paul,

Do you intend to merge this patch for 2.6.38? I did not see this in your
pull request.

Vishwa

> -----Original Message-----
> From: Paul Walmsley [mailto:paul@pwsan.com]
> Sent: Tuesday, October 05, 2010 8:48 PM
> To: Sripathy, Vishwanath
> Cc: linux-omap@vger.kernel.org; Premi, Sanjeev
> Subject: Re: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520
> for Global SW reset
>
> On Tue, 5 Oct 2010, Vishwanath BS wrote:
>
> > This patch adds comments on precatution to be taken if Global Warm
> reset is
> > used as the means to trigger sysem reset.
> >
> > Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
> > Cc: Paul Walmsley <paul@pwsan.com>
>
> Thanks, queued for 2.6.38 with Sanjeev's spelling fix.
>
>
> - Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Paul Walmsley]

Hi Vishwa

On Wed, 22 Dec 2010, Vishwanath Sripathy wrote:

> Do you intend to merge this patch for 2.6.38? I did not see this in your
> pull request.

You are right, I'm missing this one and Rajendra's 16-bit hwmod register 
patch, both of which should be in there.  I will update the branch and 
send another pull request.

- Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Paul Walmsley]

On Wed, 22 Dec 2010, Paul Walmsley wrote:

> On Wed, 22 Dec 2010, Vishwanath Sripathy wrote:
> 
> > Do you intend to merge this patch for 2.6.38? I did not see this in your
> > pull request.
> 
> You are right, I'm missing this one and Rajendra's 16-bit hwmod register 
> patch, both of which should be in there.  I will update the branch and 
> send another pull request.

(Actually Rajendra's patch went in at 2.6.37 so we are okay with that 
one)


- Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Paul Walmsley]

On Wed, 22 Dec 2010, Paul Walmsley wrote:

> On Wed, 22 Dec 2010, Vishwanath Sripathy wrote:
> 
> > Do you intend to merge this patch for 2.6.38? I did not see this in your
> > pull request.

Here's the updated patch.


- Paul


From: Vishwanath BS <vishwanath.bs@ti.com>
Date: Tue, 5 Oct 2010 19:35:34 +0530
Subject: [PATCH] OMAP3: SDRC: Add comments on Errata i520 for Global SW reset

This patch adds comments on precaution to be taken if Global Warm reset is
used as the means to trigger system reset.

Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
[paul@pwsan.com: fixed typos, one mentioned by Sanjeev]
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Sanjeev Premi <premi@ti.com>
---
 arch/arm/mach-omap2/prcm.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/arch/arm/mach-omap2/prcm.c b/arch/arm/mach-omap2/prcm.c
index c22e726..679bcd2 100644
--- a/arch/arm/mach-omap2/prcm.c
+++ b/arch/arm/mach-omap2/prcm.c
@@ -74,6 +74,34 @@ void omap_prcm_arch_reset(char mode, const char *cmd)
 		WARN_ON(1);
 	}
 
+	/*
+	 * As per Errata i520, in some cases, user will not be able to
+	 * access DDR memory after warm-reset.
+	 * This situation occurs while the warm-reset happens during a read
+	 * access to DDR memory. In that particular condition, DDR memory
+	 * does not respond to a corrupted read command due to the warm
+	 * reset occurrence but SDRC is waiting for read completion.
+	 * SDRC is not sensitive to the warm reset, but the interconnect is
+	 * reset on the fly, thus causing a misalignment between SDRC logic,
+	 * interconnect logic and DDR memory state.
+	 * WORKAROUND:
+	 * Steps to perform before a Warm reset is trigged:
+	 * 1. enable self-refresh on idle request
+	 * 2. put SDRC in idle
+	 * 3. wait until SDRC goes to idle
+	 * 4. generate SW reset (Global SW reset)
+	 *
+	 * Steps to be performed after warm reset occurs (in bootloader):
+	 * if HW warm reset is the source, apply below steps before any
+	 * accesses to SDRAM:
+	 * 1. Reset SMS and SDRC and wait till reset is complete
+	 * 2. Re-initialize SMS, SDRC and memory
+	 *
+	 * NOTE: Above work around is required only if arch reset is implemented
+	 * using Global SW reset(GLOBAL_SW_RST). DPLL3 reset does not need
+	 * the WA since it resets SDRC as well as part of cold reset.
+	 */
+
 	/* XXX should be moved to some OMAP2/3 specific code */
 	omap2_prm_set_mod_reg_bits(OMAP_RST_DPLL3_MASK, prcm_offs,
 				   OMAP2_RM_RSTCTRL);
-- 
1.7.2.3

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Vishwanath Sripathy]

Paul,

Do you intend to merge this patch for 2.6.38? I did not see this in your
pull request.

Vishwa

> -----Original Message-----
> From: Paul Walmsley [mailto:paul@pwsan.com]
> Sent: Tuesday, October 05, 2010 8:48 PM
> To: Sripathy, Vishwanath
> Cc: linux-omap@vger.kernel.org; Premi, Sanjeev
> Subject: Re: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520
> for Global SW reset
>
> On Tue, 5 Oct 2010, Vishwanath BS wrote:
>
> > This patch adds comments on precatution to be taken if Global Warm
> reset is
> > used as the means to trigger sysem reset.
> >
> > Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
> > Cc: Paul Walmsley <paul@pwsan.com>
>
> Thanks, queued for 2.6.38 with Sanjeev's spelling fix.
>
>
> - Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Sripathy, Vishwanath]

Paul,

> -----Original Message-----
> From: Paul Walmsley [mailto:paul@pwsan.com]
> Sent: Tuesday, October 05, 2010 8:48 PM
> To: Sripathy, Vishwanath
> Cc: linux-omap@vger.kernel.org; Premi, Sanjeev
> Subject: Re: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520
> for Global SW reset
>
> On Tue, 5 Oct 2010, Vishwanath BS wrote:
>
> > This patch adds comments on precatution to be taken if Global Warm
> reset is
> > used as the means to trigger sysem reset.
> >
> > Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
> > Cc: Paul Walmsley <paul@pwsan.com>
>
> Thanks, queued for 2.6.38 with Sanjeev's spelling fix.

Do you intend to merge this patch for 2.6.38? I did not see this in
your pull request.

Vishwa

>
>
> - Paul

RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520 for Global SW reset

[Vishwanath Sripathy]

Paul,
Pls ignore my other 2 emails. There were some issues in my mailbox.

Vishwa

> -----Original Message-----
> From: Sripathy, Vishwanath [mailto:vishwanath.bs@ti.com]
> Sent: Wednesday, December 22, 2010 1:58 PM
> To: Paul Walmsley
> Cc: linux-omap@vger.kernel.org; Premi, Sanjeev
> Subject: RE: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520
> for Global SW reset
>
> Paul,
>
> > -----Original Message-----
> > From: Paul Walmsley [mailto:paul@pwsan.com]
> > Sent: Tuesday, October 05, 2010 8:48 PM
> > To: Sripathy, Vishwanath
> > Cc: linux-omap@vger.kernel.org; Premi, Sanjeev
> > Subject: Re: [PATCHv3] OMAP3: SDRC : Add comments on Errata i520
> > for Global SW reset
> >
> > On Tue, 5 Oct 2010, Vishwanath BS wrote:
> >
> > > This patch adds comments on precatution to be taken if Global
> Warm
> > reset is
> > > used as the means to trigger sysem reset.
> > >
> > > Signed-off-by: Vishwanath BS <vishwanath.bs@ti.com>
> > > Cc: Paul Walmsley <paul@pwsan.com>
> >
> > Thanks, queued for 2.6.38 with Sanjeev's spelling fix.
>
> Do you intend to merge this patch for 2.6.38? I did not see this in
> your pull request.
>
> Vishwa
>
> >
> >
> > - Paul