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Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for keystone-nand"

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  Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for  keystone-nand" Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-29 17:10 +0200
    Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for  keystone-nand" Sekhar Nori <nsekhar@ti.com> - 2017-03-30 09:50 +0200
      Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for  keystone-nand" Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-30 12:10 +0200
        Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for  keystone-nand" Sekhar Nori <nsekhar@ti.com> - 2017-03-30 12:20 +0200
          Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for  keystone-nand" Boris Brezillon <boris.brezillon@free-electrons.com> - 2017-03-30 13:50 +0200

#1612022 — Re: [PATCH] Revert "mtd: davinci-nand: disable subpage write for keystone-nand"

On Mon, 27 Mar 2017 15:56:55 +0530
Sekhar Nori <nsekhar@ti.com> wrote:

> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
> 
> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
> engine in 4bit hwctl") using subpage and 4bit HWECC works.
> 
> Revert the original workaround made for this. Tested with
> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
> 
> The addition of keystone specific compatible to davinci_nand_of_match[]
> contained in original commit is retained.

Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
You might break existing systems using UBI, because UBI detects the
sub-page write feature and decides to place the VID header at a
different position depending on that.
To sum-up, you're likely to break users that have already flashed a UBI
image with the old driver.

If you want to re-enable sub-page writes, just switch back to the
"ti,davinci-nand" compatible.

> 
> Cc: Muralidharan Karicheri <m-karicheri2@ti.com>
> Cc: Franklin S Cooper Jr <fcooper@ti.com>
> Signed-off-by: Sekhar Nori <nsekhar@ti.com>
> ---
>  drivers/mtd/nand/davinci_nand.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> index 27fa8b87cd5f..56c4afed8d74 100644
> --- a/drivers/mtd/nand/davinci_nand.c
> +++ b/drivers/mtd/nand/davinci_nand.c
> @@ -580,11 +580,6 @@ static struct davinci_nand_pdata
>  		if (of_property_read_bool(pdev->dev.of_node,
>  			"ti,davinci-nand-use-bbt"))
>  			pdata->bbt_options = NAND_BBT_USE_FLASH;
> -
> -		if (of_device_is_compatible(pdev->dev.of_node,
> -					    "ti,keystone-nand")) {
> -			pdata->options |= NAND_NO_SUBPAGE_WRITE;
> -		}
>  	}
>  
>  	return dev_get_platdata(&pdev->dev);

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#1612680

Hi Boris,

On Wednesday 29 March 2017 08:33 PM, Boris Brezillon wrote:
> On Mon, 27 Mar 2017 15:56:55 +0530
> Sekhar Nori <nsekhar@ti.com> wrote:
> 
>> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
>>
>> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
>> engine in 4bit hwctl") using subpage and 4bit HWECC works.
>>
>> Revert the original workaround made for this. Tested with
>> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
>>
>> The addition of keystone specific compatible to davinci_nand_of_match[]
>> contained in original commit is retained.
> 
> Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
> You might break existing systems using UBI, because UBI detects the
> sub-page write feature and decides to place the VID header at a
> different position depending on that.
> To sum-up, you're likely to break users that have already flashed a UBI
> image with the old driver.

Okay, I didn't realize that.

> If you want to re-enable sub-page writes, just switch back to the
> "ti,davinci-nand" compatible.

How about a comment on top of the disable subpage write code explaining 
that its not really needed anymore ? Something like this patch:

---8<---
From: Sekhar Nori <nsekhar@ti.com>
Date: Thu, 30 Mar 2017 13:08:30 +0530
Subject: [PATCH] mtd: nand: davinci: add comment on NAND subpage write status
 on keystone

Add a comment clarifying that NAND subpage write on keystone works,
but is not being enabled in the interest of backward compatibility.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
---
 drivers/mtd/nand/davinci_nand.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index 27fa8b87cd5f..5bf8be1cfc8c 100644
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -581,6 +581,17 @@ static struct davinci_nand_pdata
 			"ti,davinci-nand-use-bbt"))
 			pdata->bbt_options = NAND_BBT_USE_FLASH;
 
+		/*
+		 * Since kernel v4.8, this driver has been fixed to enable
+		 * use of 4-bit hardware ECC with subpages and verified on
+		 * TI's keystone EVMs (K2L, K2HK and K2E).
+		 * However, in the interest of not breaking systems using
+		 * existing UBI partitions, sub-page writes are not being
+		 * (re)enabled. If you want to use subpage writes on Keystone
+		 * platforms (i.e. do not have any existing UBI partitions),
+		 * then remove the if() block below or pass "ti,davinci-nand"
+		 * as the compatible in your device-tree file.
+		 */
 		if (of_device_is_compatible(pdev->dev.of_node,
 					    "ti,keystone-nand")) {
 			pdata->options |= NAND_NO_SUBPAGE_WRITE;
-- 
2.9.0

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#1612845

On Thu, 30 Mar 2017 13:13:58 +0530
Sekhar Nori <nsekhar@ti.com> wrote:

> Hi Boris,
> 
> On Wednesday 29 March 2017 08:33 PM, Boris Brezillon wrote:
> > On Mon, 27 Mar 2017 15:56:55 +0530
> > Sekhar Nori <nsekhar@ti.com> wrote:
> >   
> >> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
> >>
> >> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
> >> engine in 4bit hwctl") using subpage and 4bit HWECC works.
> >>
> >> Revert the original workaround made for this. Tested with
> >> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
> >>
> >> The addition of keystone specific compatible to davinci_nand_of_match[]
> >> contained in original commit is retained.  
> > 
> > Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
> > You might break existing systems using UBI, because UBI detects the
> > sub-page write feature and decides to place the VID header at a
> > different position depending on that.
> > To sum-up, you're likely to break users that have already flashed a UBI
> > image with the old driver.  
> 
> Okay, I didn't realize that.
> 
> > If you want to re-enable sub-page writes, just switch back to the
> > "ti,davinci-nand" compatible.  
> 
> How about a comment on top of the disable subpage write code explaining 
> that its not really needed anymore ? Something like this patch:
> 
> ---8<---
> From: Sekhar Nori <nsekhar@ti.com>
> Date: Thu, 30 Mar 2017 13:08:30 +0530
> Subject: [PATCH] mtd: nand: davinci: add comment on NAND subpage write status
>  on keystone
> 
> Add a comment clarifying that NAND subpage write on keystone works,
> but is not being enabled in the interest of backward compatibility.
> 
> Signed-off-by: Sekhar Nori <nsekhar@ti.com>
> ---
>  drivers/mtd/nand/davinci_nand.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> index 27fa8b87cd5f..5bf8be1cfc8c 100644
> --- a/drivers/mtd/nand/davinci_nand.c
> +++ b/drivers/mtd/nand/davinci_nand.c
> @@ -581,6 +581,17 @@ static struct davinci_nand_pdata
>  			"ti,davinci-nand-use-bbt"))
>  			pdata->bbt_options = NAND_BBT_USE_FLASH;
>  
> +		/*
> +		 * Since kernel v4.8, this driver has been fixed to enable
> +		 * use of 4-bit hardware ECC with subpages and verified on
> +		 * TI's keystone EVMs (K2L, K2HK and K2E).
> +		 * However, in the interest of not breaking systems using
> +		 * existing UBI partitions, sub-page writes are not being
> +		 * (re)enabled. If you want to use subpage writes on Keystone
> +		 * platforms (i.e. do not have any existing UBI partitions),
> +		 * then remove the if() block below or pass "ti,davinci-nand"
> +		 * as the compatible in your device-tree file.

Hm, I'm not sure we should suggest to remove these lines from the code.
Just suggest to use "ti,davinci-nand" compatible.
If you're okay with that, no need to resend, I can rework the comment
accordingly before applying the patch.

Another long term solution: if UBI is the only MTD user to be
incompatible when sub-page write is activated/deactivated, maybe we can
relax the checks in UBI to allow it to attach a partition where VID
header offset is at mtd->writesize instead of
mtd->writesize >> mtd->subpage_sft.

I'll let Richard comment on that solution though.

> +		 */
>  		if (of_device_is_compatible(pdev->dev.of_node,
>  					    "ti,keystone-nand")) {
>  			pdata->options |= NAND_NO_SUBPAGE_WRITE;

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#1612881

On Thursday 30 March 2017 03:30 PM, Boris Brezillon wrote:
> On Thu, 30 Mar 2017 13:13:58 +0530
> Sekhar Nori <nsekhar@ti.com> wrote:
> 
>> Hi Boris,
>>
>> On Wednesday 29 March 2017 08:33 PM, Boris Brezillon wrote:
>>> On Mon, 27 Mar 2017 15:56:55 +0530
>>> Sekhar Nori <nsekhar@ti.com> wrote:
>>>   
>>>> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
>>>>
>>>> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
>>>> engine in 4bit hwctl") using subpage and 4bit HWECC works.
>>>>
>>>> Revert the original workaround made for this. Tested with
>>>> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
>>>>
>>>> The addition of keystone specific compatible to davinci_nand_of_match[]
>>>> contained in original commit is retained.  
>>>
>>> Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
>>> You might break existing systems using UBI, because UBI detects the
>>> sub-page write feature and decides to place the VID header at a
>>> different position depending on that.
>>> To sum-up, you're likely to break users that have already flashed a UBI
>>> image with the old driver.  
>>
>> Okay, I didn't realize that.
>>
>>> If you want to re-enable sub-page writes, just switch back to the
>>> "ti,davinci-nand" compatible.  
>>
>> How about a comment on top of the disable subpage write code explaining 
>> that its not really needed anymore ? Something like this patch:
>>
>> ---8<---
>> From: Sekhar Nori <nsekhar@ti.com>
>> Date: Thu, 30 Mar 2017 13:08:30 +0530
>> Subject: [PATCH] mtd: nand: davinci: add comment on NAND subpage write status
>>  on keystone
>>
>> Add a comment clarifying that NAND subpage write on keystone works,
>> but is not being enabled in the interest of backward compatibility.
>>
>> Signed-off-by: Sekhar Nori <nsekhar@ti.com>
>> ---
>>  drivers/mtd/nand/davinci_nand.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
>> index 27fa8b87cd5f..5bf8be1cfc8c 100644
>> --- a/drivers/mtd/nand/davinci_nand.c
>> +++ b/drivers/mtd/nand/davinci_nand.c
>> @@ -581,6 +581,17 @@ static struct davinci_nand_pdata
>>  			"ti,davinci-nand-use-bbt"))
>>  			pdata->bbt_options = NAND_BBT_USE_FLASH;
>>  
>> +		/*
>> +		 * Since kernel v4.8, this driver has been fixed to enable
>> +		 * use of 4-bit hardware ECC with subpages and verified on
>> +		 * TI's keystone EVMs (K2L, K2HK and K2E).
>> +		 * However, in the interest of not breaking systems using
>> +		 * existing UBI partitions, sub-page writes are not being
>> +		 * (re)enabled. If you want to use subpage writes on Keystone
>> +		 * platforms (i.e. do not have any existing UBI partitions),
>> +		 * then remove the if() block below or pass "ti,davinci-nand"
>> +		 * as the compatible in your device-tree file.
> 
> Hm, I'm not sure we should suggest to remove these lines from the code.
> Just suggest to use "ti,davinci-nand" compatible.

Thats fine with me. Today, this if() block is the only place where
ti,keystone-nand is used. If in future it gets used for something else
(yet unknown), then the comment might start to get misleading. Thats why
just removing the code seemed like a safer option to me.

But the main intention was to document that subpage is not really broken
on K2 platform. So, what you suggest will do as well.

Thanks,
Sekhar

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#1612979

On Thu, 30 Mar 2017 15:38:54 +0530
Sekhar Nori <nsekhar@ti.com> wrote:

> On Thursday 30 March 2017 03:30 PM, Boris Brezillon wrote:
> > On Thu, 30 Mar 2017 13:13:58 +0530
> > Sekhar Nori <nsekhar@ti.com> wrote:
> >   
> >> Hi Boris,
> >>
> >> On Wednesday 29 March 2017 08:33 PM, Boris Brezillon wrote:  
> >>> On Mon, 27 Mar 2017 15:56:55 +0530
> >>> Sekhar Nori <nsekhar@ti.com> wrote:
> >>>     
> >>>> This partly reverts commit 28c015a9daabe4ed3aeb0ccf669a3f1c2b8b81d5.
> >>>>
> >>>> Since f6d7c1b5598b ("mtd: nand: davinci: Reinitialize the HW ECC
> >>>> engine in 4bit hwctl") using subpage and 4bit HWECC works.
> >>>>
> >>>> Revert the original workaround made for this. Tested with
> >>>> mtd_subpagetest and UBIFS on K2E, K2HK, K2L EVMs.
> >>>>
> >>>> The addition of keystone specific compatible to davinci_nand_of_match[]
> >>>> contained in original commit is retained.    
> >>>
> >>> Hm, it sounds like a bad idea to re-enable sub-page writes afterwards.
> >>> You might break existing systems using UBI, because UBI detects the
> >>> sub-page write feature and decides to place the VID header at a
> >>> different position depending on that.
> >>> To sum-up, you're likely to break users that have already flashed a UBI
> >>> image with the old driver.    
> >>
> >> Okay, I didn't realize that.
> >>  
> >>> If you want to re-enable sub-page writes, just switch back to the
> >>> "ti,davinci-nand" compatible.    
> >>
> >> How about a comment on top of the disable subpage write code explaining 
> >> that its not really needed anymore ? Something like this patch:
> >>
> >> ---8<---
> >> From: Sekhar Nori <nsekhar@ti.com>
> >> Date: Thu, 30 Mar 2017 13:08:30 +0530
> >> Subject: [PATCH] mtd: nand: davinci: add comment on NAND subpage write status
> >>  on keystone
> >>
> >> Add a comment clarifying that NAND subpage write on keystone works,
> >> but is not being enabled in the interest of backward compatibility.
> >>
> >> Signed-off-by: Sekhar Nori <nsekhar@ti.com>
> >> ---
> >>  drivers/mtd/nand/davinci_nand.c | 11 +++++++++++
> >>  1 file changed, 11 insertions(+)
> >>
> >> diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
> >> index 27fa8b87cd5f..5bf8be1cfc8c 100644
> >> --- a/drivers/mtd/nand/davinci_nand.c
> >> +++ b/drivers/mtd/nand/davinci_nand.c
> >> @@ -581,6 +581,17 @@ static struct davinci_nand_pdata
> >>  			"ti,davinci-nand-use-bbt"))
> >>  			pdata->bbt_options = NAND_BBT_USE_FLASH;
> >>  
> >> +		/*
> >> +		 * Since kernel v4.8, this driver has been fixed to enable
> >> +		 * use of 4-bit hardware ECC with subpages and verified on
> >> +		 * TI's keystone EVMs (K2L, K2HK and K2E).
> >> +		 * However, in the interest of not breaking systems using
> >> +		 * existing UBI partitions, sub-page writes are not being
> >> +		 * (re)enabled. If you want to use subpage writes on Keystone
> >> +		 * platforms (i.e. do not have any existing UBI partitions),
> >> +		 * then remove the if() block below or pass "ti,davinci-nand"
> >> +		 * as the compatible in your device-tree file.  
> > 
> > Hm, I'm not sure we should suggest to remove these lines from the code.
> > Just suggest to use "ti,davinci-nand" compatible.  

Can you send a separate patch so that it appears on its own in
patchwork?

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