Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Kalle Valo]

Alagu Sankar  writes:

> On 2017-12-22 21:38, Kalle Valo wrote:
>> silexcom...@gmail.com writes:
>>
>>> From: Alagu Sankar 
>>>
>>> Some SD host controllers still need bounce buffers for SDIO data
>>> transfers. While the transfers worked fine on x86 platforms,
>>> this is found to be required for i.MX6 based systems.
>>>
>>> Changes are similar to and derived from the ath6kl sdio driver.
>>>
>>> Signed-off-by: Alagu Sankar 
>>
>> Why is the bounce buffer needed exactly, what are the symptoms etc? To
>> me this sounds like an ugly workaround for a SDIO controller driver
>> bug.
>
> We faced problems with i.MX6. The authentication frame sent by the
> driver never reached the air. The host driver accepted the buffer, but
> did not send out the packet to the sdio module. No errors reported
> anywhere, but the buffer is not accepted due to alignment.

So what kind of alignment works with i.MX6 and how are the packets
aligned by ath10k? Of course, this might be still a bug in ath10k but
most likely it's elsewhere and should be properly investigated. There
must be a much better approach to handle this problem.

> The same driver however works fine without bounce buffer on x86
> platform with stdhci drivers. To make it compliant with all host
> controllers, we introduced the bounce buffers, similar to what was
> done in ath6kl_sdio drivers.

That bounce buffer was horrible in ath6kl and with the bounce buffer you
are forcing all working platforms to suffer from a copy of every packet.
And ath10k is getting so complex that we really need to keep the code as
simple as possible to keep it maintainable.

-- 
Kalle Valo
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Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Adrian Chadd]

[top post for emphasis]

Arend is right. You won't be the only driver which has issues with a
controller that doesn't handle non-aligned data payloads. Please push
it into the stack or the controller side, but not in the driver side.
That'll be a forever game of whack-a-mole.


-adrian

(I'm living this dream right now and it's unfun)



On 27 December 2017 at 10:49, Arend van Spriel
 wrote:
> On 12/25/2017 1:26 PM, Alagu Sankar wrote:
>>
>> On 2017-12-22 21:38, Kalle Valo wrote:
>>>
>>> silexcom...@gmail.com writes:
>>>
 From: Alagu Sankar 

 Some SD host controllers still need bounce buffers for SDIO data
 transfers. While the transfers worked fine on x86 platforms,
 this is found to be required for i.MX6 based systems.

 Changes are similar to and derived from the ath6kl sdio driver.

 Signed-off-by: Alagu Sankar 
>>>
>>>
>>> Why is the bounce buffer needed exactly, what are the symptoms etc? To
>>> me this sounds like an ugly workaround for a SDIO controller driver bug.
>>
>>
>> We faced problems with i.MX6. The authentication frame sent by the
>> driver never reached the air. The host driver accepted the buffer, but
>> did not send out the packet to the sdio module. No errors reported
>> anywhere, but the buffer is not accepted due to alignment. The same
>> driver however works fine without bounce buffer on x86 platform with
>> stdhci drivers. To make it compliant with all host controllers, we
>> introduced the bounce buffers, similar to what was done in ath6kl_sdio
>> drivers.
>
>
> As mentioned by Adrian the comment from Kalle is that you are solving an
> issue caused by the sdio host controller. Although strictly speaking it may
> not be a driver bug, but a requirement of the host controller hardware.
> Either way it seems the obvious place to solve this is in the sdio host
> controller driver to which the issue applies. Or make it a generic quirk
> which can be enabled for sdio host controller drivers that need it. However,
> there may reasons to do it in the networking driver. For instance, the
> buffer you want to transfer might be the data buffer of an sk_buff you got
> from the networking stack and you want to have a zero-copy solution towards
> the wireless device.
>
> Your solution checks for 4-byte alignment which is a requirement for ADMA as
> per SDIO spec. However, I have come across host controllers which have
> different alignment requirements. Also when CONFIG_ARCH_DMA_ADDR_T_64BIT is
> enabled the alignment changes from 4 to 8 bytes. So it seems you are solving
> a specific case you have come across, but you may want to design for more
> flexibility.
>
> Hope this helps.
>
> Regards,
> Arend

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Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Arend van Spriel]

On 12/25/2017 1:26 PM, Alagu Sankar wrote:

On 2017-12-22 21:38, Kalle Valo wrote:

silexcom...@gmail.com writes:


From: Alagu Sankar 

Some SD host controllers still need bounce buffers for SDIO data
transfers. While the transfers worked fine on x86 platforms,
this is found to be required for i.MX6 based systems.

Changes are similar to and derived from the ath6kl sdio driver.

Signed-off-by: Alagu Sankar 


Why is the bounce buffer needed exactly, what are the symptoms etc? To
me this sounds like an ugly workaround for a SDIO controller driver bug.


We faced problems with i.MX6. The authentication frame sent by the
driver never reached the air. The host driver accepted the buffer, but
did not send out the packet to the sdio module. No errors reported
anywhere, but the buffer is not accepted due to alignment. The same
driver however works fine without bounce buffer on x86 platform with
stdhci drivers. To make it compliant with all host controllers, we
introduced the bounce buffers, similar to what was done in ath6kl_sdio
drivers.


As mentioned by Adrian the comment from Kalle is that you are solving an 
issue caused by the sdio host controller. Although strictly speaking it 
may not be a driver bug, but a requirement of the host controller 
hardware. Either way it seems the obvious place to solve this is in the 
sdio host controller driver to which the issue applies. Or make it a 
generic quirk which can be enabled for sdio host controller drivers that 
need it. However, there may reasons to do it in the networking driver. 
For instance, the buffer you want to transfer might be the data buffer 
of an sk_buff you got from the networking stack and you want to have a 
zero-copy solution towards the wireless device.


Your solution checks for 4-byte alignment which is a requirement for 
ADMA as per SDIO spec. However, I have come across host controllers 
which have different alignment requirements. Also when 
CONFIG_ARCH_DMA_ADDR_T_64BIT is enabled the alignment changes from 4 to 
8 bytes. So it seems you are solving a specific case you have come 
across, but you may want to design for more flexibility.


Hope this helps.

Regards,
Arend

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Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Adrian Chadd]

Hi,

I think Kalle is pointing out that maybe it's the SDHCI driver
responsibility to do the bounce buffering?



-adrian

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Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Alagu Sankar]

On 2017-12-22 21:38, Kalle Valo wrote:

silexcom...@gmail.com writes:


From: Alagu Sankar 

Some SD host controllers still need bounce buffers for SDIO data
transfers. While the transfers worked fine on x86 platforms,
this is found to be required for i.MX6 based systems.

Changes are similar to and derived from the ath6kl sdio driver.

Signed-off-by: Alagu Sankar 


Why is the bounce buffer needed exactly, what are the symptoms etc? To
me this sounds like an ugly workaround for a SDIO controller driver 
bug.


We faced problems with i.MX6. The authentication frame sent by the 
driver never reached the air. The host driver accepted the buffer, but 
did not send out the packet to the sdio module. No errors reported 
anywhere, but the buffer is not accepted due to alignment. The same 
driver however works fine without bounce buffer on x86 platform with 
stdhci drivers. To make it compliant with all host controllers, we 
introduced the bounce buffers, similar to what was done in ath6kl_sdio 
drivers.


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Re: [PATCH 03/11] ath10k_sdio: DMA bounce buffers for read write

[Kalle Valo]

silexcom...@gmail.com writes:

> From: Alagu Sankar 
>
> Some SD host controllers still need bounce buffers for SDIO data
> transfers. While the transfers worked fine on x86 platforms,
> this is found to be required for i.MX6 based systems.
>
> Changes are similar to and derived from the ath6kl sdio driver.
>
> Signed-off-by: Alagu Sankar 

Why is the bounce buffer needed exactly, what are the symptoms etc? To
me this sounds like an ugly workaround for a SDIO controller driver bug.

-- 
Kalle Valo
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