Date:	Fri, 19 Feb 2016 11:48:35 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	<davem@...emloft.net>
Subject: Re: [PATCH v1 1/4] net: ti: netcp: restore get/set_pad_info()
 functionality

On 02/19/2016 11:41 AM, Arnd Bergmann wrote:
> On Friday 19 February 2016 10:48:30 Murali Karicheri wrote:
>> On 02/19/2016 09:41 AM, Arnd Bergmann wrote:
>>> On Thursday 18 February 2016 14:46:14 Murali Karicheri wrote:
>>>> From: Arnd Bergmann <arnd@...db.de>
>>>>
>>>> The commit 899077791403 ("netcp: try to reduce type confusion in
>>>> descriptors") introduces a regression in Kernel 4.5-rc1 and it breaks
>>>> get/set_pad_info() functionality.
>>>>
>>>> The TI NETCP driver uses pad0 and pad1 fields of knav_dma_desc to
>>>> store DMA/MEM buffer pointer and buffer size respectively. And in both
>>>> cases for Keystone 2 the pointer type size is 32 bit regardless of
>>>> LAPE enabled or not, because CONFIG_ARCH_DMA_ADDR_T_64BIT originally
>>>> is not expected to be defined.
>>>>
>>>>                      !LAPE   LPAE
>>>> sizeof(void*)                32bit   32bit
>>>> sizeof(dma_addr_t)   32bit   32bit
>>>> sizeof(phys_addr_t)  32bit   64bit
>>>
>>> As this was never relevant or true, I don't think it needs to be
>>> mentioned here, it just confuses things. Please just assume that
>>> dma_addr_t can be 64-bit wide, but will only contain 32-bit
>>> numbers on keystone.
>>>
>>
>> I can remove this from the commit description and re-send.
> 
> Ok
> 
>>>> Unfortunately, above commit changed buffer's pointers save/restore
>>>> code (get/set_pad_info()) and added intermediate conversation to u64
>>>> which works incorrectly on 32bit Keystone 2 and causes TI NETCP driver
>>>> crash in RX/TX path due to "Unable to handle kernel NULL pointer"
>>>> exception. This issue was reported and discussed in [1].
>>>
>>> Have you been able to figure out why it actually broke? I'd still
>>> like to know.
>>>
>> As Grygorii is out of office until Monday, I would like to step in.
>> I will take some time today to try review the reverted changes for
>> failure reason and get back. But as you have agreed in the discussion
>> at https://www.mail-archive.com/netdev@vger.kernel.org/msg96311.html
>> Can we fix the regression by applying this patch and rest of the series
>> if it looks good? If I need to separate this from rest of the series,
>> let me know and I can take care of that.
> 
> Yes, sounds fine.
> 
>>>> Hence, fix it by partially reverting above commit and restoring
>>>> get/set_pad_info() functionality as it was before.
>>>>
>>>> [1] https://www.mail-archive.com/netdev@vger.kernel.org/msg95361.html
>>>> Cc: Wingman Kwok <w-kwok2@...com>
>>>> Cc: Mugunthan V N <mugunthanvnm@...com>
>>>> CC: David Laight <David.Laight@...LAB.COM>
>>>> Reported-by: Franklin S Cooper Jr <fcooper@...com>
>>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>>
>>> I don't think I sent this patch with a 'Signed-off-by', did I?
>>> (I could be misremembering that).
>>>
>>
>> I think you had agreed based on what I read at
>> https://www.mail-archive.com/netdev@vger.kernel.org/msg96311.html
>>
>> reproduced below for your convenience.
>> =============================================================================
>>
>>> What I could do now is update your/my patch as i mentioned in [1]
>>> and re-send it at the weekend (with your authorship and my signoff).
>>> Do you agree?
>>>
>>>
>>> [1] https://www.mail-archive.com/netdev@vger.kernel.org/msg95831.html
>>
>> Yes, let's do that in the meantime. I can also make sure that that
>> the driver doesn't build on 64-bit, just in case.
>> =============================================================================
>>
>> Hope I can keep your sign-off when I re-send this. Please confirm.
> 
> The most important part here is that you don't add a "Signed-off-by"
> tag unless it was provided by that person as part of the submission.
> 
> I'm slightly uncomfortable with having my Signed-off-by as the first
> one when I did not write the changelog myself, so I'd prefer if
> you just add my Acked-by once I provide that. If that doesn't
> work for you, let's follow up in private to sort it out.
> 
Ok. I will remove it.

> 	Arnd
> 


-- 
Murali Karicheri
Linux Kernel, Keystone

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