linux-kernel - Re: [PATCH v2 0/2] net: ethernet: ti: cpsw: delete rx

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Date:	Wed, 8 Jun 2016 18:11:33 -0500
From:	Schuyler Patton <spatton@...com>
To:	Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
	<mugunthanvnm@...com>, <linux-kernel@...r.kernel.org>
CC:	<grygorii.strashko@...com>, <linux-omap@...r.kernel.org>,
	<netdev@...r.kernel.org>, <robh+dt@...nel.org>,
	<pawel.moll@....com>, <mark.rutland@....com>,
	<ijc+devicetree@...lion.org.uk>, <galak@...eaurora.org>,
	<bcousson@...libre.com>, <tony@...mide.com>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] net: ethernet: ti: cpsw: delete rx_descs property



On 06/08/2016 09:06 AM, Ivan Khoronzhuk wrote:
>
>
> On 08.06.16 17:01, Ivan Khoronzhuk wrote:
>> Hi Schuyer,
>>
>> On 07.06.16 18:26, Schuyler Patton wrote:
>>> Hi,
>>>
>>> On 06/07/2016 08:59 AM, Ivan Khoronzhuk wrote:
>>>> There is no reason in rx_descs property because davinici_cpdma
>>>> driver splits pool of descriptors equally between tx and rx channels.
>>>> So, this patch series makes driver to use available number of
>>>> descriptors for rx channels.
>>>
>>> I agree with the idea of consolidating how the descriptors are 
>>> defined because of
>>> the two variable components, number and size of the pool can be 
>>> confusing to
>>> end users. I would like to request to change how it is being 
>>> proposed here.
>>>
>>> I think the number of descriptors should be left in the device tree 
>>> source file as
>>> is and remove the BD size variable and have the driver calculate the 
>>> size of the
>>> pool necessary to support the descriptor request. From an user 
>>> perspective it is
>>> easier I think to be able to list the number of descriptors 
>>> necessary vs. the size
>>> of the pool.
>>>
>>> Since the patch series points out how it is used so in the driver so 
>>> to make that
>>> consistent is perhaps change rx_descs to total_descs.
>>>
>>> Regards,
>>> Schuyler
>>
>> The DT entry for cpsw doesn't have property for size of the pool.
>> It contains only BD ram size, if you mean this. The size of the pool is
>> software decision. Current version of DT entry contain only rx desc 
>> number.
>> That is not correct, as it depends on the size of the descriptor, 
>> which is also
>> h/w parameter. The DT entry has to describe only h/w part and 
>> shouldn't contain
>> driver implementation details, and I'm looking on it from this 
>> perspective.
>>
>> Besides, rx_descs describes only rx number of descriptors, that are 
>> taken from
>> the same pool as tx descriptors, and setting rx desc to some new 
>> value doesn't
>> mean that rest of them are freed for tx. Also, I'm going to send 
>> series that
>> adds multi channel support to the driver, and in this case, splitting 
>> of the
>> pool will be more sophisticated than now, after what setting those 
>> parameters
>> for user (he should do this via device tree) can be even more 
>> confusing. But,
> should -> shouldn't
>
>> as it's supposed, it's software decision that shouldn't leak to the DT.

If this rx-desc field is removed how will the number of descriptors be set?

This field has been used to increase the number of descriptors so high
volume short packets are not dropped due to descriptor exhaustion. The 
current
default number of 64 rx descriptors is too low for gigabit networks. 
Some users
have a strong requirement for zero loss of UDP packets setting this 
field to a
larger number and setting the descriptors off-chip was a means to solve
the problem.

>>
>>
>>>>
>>>> Based on master branch
>>>>
>>>> Since v1:
>>>> - separate device tree and driver patches
>>>> - return number of rx buffers from cpdma driver
>>>>
>>>> Ivan Khoronzhuk (2):
>>>>    net: ethernet: ti: cpsw: remove rx_descs property
>>>>    Documentation: DT: cpsw: remove rx_descs property
>>>>
>>>>   Documentation/devicetree/bindings/net/cpsw.txt |  1 -
>>>>   arch/arm/boot/dts/am33xx.dtsi                  |  1 -
>>>>   arch/arm/boot/dts/am4372.dtsi                  |  1 -
>>>>   arch/arm/boot/dts/dm814x.dtsi                  |  1 -
>>>>   arch/arm/boot/dts/dra7.dtsi                    |  1 -
>>>>   drivers/net/ethernet/ti/cpsw.c                 | 13 +++----------
>>>>   drivers/net/ethernet/ti/cpsw.h                 |  1 -
>>>>   drivers/net/ethernet/ti/davinci_cpdma.c        |  6 ++++++
>>>>   drivers/net/ethernet/ti/davinci_cpdma.h        |  1 +
>>>>   9 files changed, 10 insertions(+), 16 deletions(-)
>>>>
>>>
>>
>