Subject: Re: [PATCH] net: ethernet: ti: cpsw: remove rx_descs property

From: Grygorii Strashko <[email-masked]>
Date: Fri, 3 Jun 2016 22:13:36 +0300

On 06/03/2016 09:25 PM, Ivan Khoronzhuk wrote:
> 
> 
> On 03.06.16 19:50, Grygorii Strashko wrote:
>> On 06/03/2016 01:43 AM, Ivan Khoronzhuk wrote:
>>> There is no reason to hold s/w dependent parameter in device tree.
>>> Even more, there is no reason in this parameter because davinici_cpdma
>>> driver splits pool of descriptors equally between tx and rx channels.
>>> That is, if number of descriptors 256, 128 of them are for rx
>>> channels. While receiving, the descriptor is freed to the pool and
>>> then allocated with new skb. And if in DT the "rx_descs" is set to
>>> 64, then 128 - 64 = 64 descriptors are always in the pool and cannot
>>> be used, for tx, for instance. It's not correct resource usage,
>>> better to set it to half of pool, then the rx pool can be used in
>>> full. It will not have any impact on performance, as anyway, the
>>> "redundant" descriptors were unused.
>>>
>>> Signed-off-by: Ivan Khoronzhuk <[email-masked]>
>>> ---
>>>
>>> Based on master
>>>
>>>   Documentation/devicetree/bindings/net/cpsw.txt |  3 ---
>>>   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 -
>>
>>
>> Pls, split DT and non-DT changes, seems code changes should go first.
> Ok.
> 
>>
>>>   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(+), 18 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/cpsw.txt 
>>> b/Documentation/devicetree/bindings/net/cpsw.txt
>>> index 0ae0649..5fe6239 100644
>>> --- a/Documentation/devicetree/bindings/net/cpsw.txt
>>> +++ b/Documentation/devicetree/bindings/net/cpsw.txt
>>> @@ -15,7 +15,6 @@ Required properties:
>>>   - cpdma_channels     : Specifies number of channels in CPDMA
>>>   - ale_entries        : Specifies No of entries ALE can hold
>>>   - bd_ram_size        : Specifies internal descriptor RAM size
>>> -- rx_descs        : Specifies number of Rx descriptors
>>>   - mac_control        : Specifies Default MAC control register content
>>>                 for the specific platform
>>>   - slaves        : Specifies number for slaves
>>> @@ -70,7 +69,6 @@ Examples:
>>
>> [....]
>>
>>>               slaves = <2>;
>>>               active_slave = <0>;
>>> diff --git a/drivers/net/ethernet/ti/cpsw.c 
>>> b/drivers/net/ethernet/ti/cpsw.c
>>> index 4b08a2f..635be3e 100644
>>> --- a/drivers/net/ethernet/ti/cpsw.c
>>> +++ b/drivers/net/ethernet/ti/cpsw.c
>>> @@ -1277,6 +1277,7 @@ static int cpsw_ndo_open(struct net_device *ndev)
>>>                     ALE_ALL_PORTS, ALE_ALL_PORTS, 0, 0);
>>>
>>>       if (!cpsw_common_res_usage_state(priv)) {
>>> +        int buf_num;
>>>           struct cpsw_priv *priv_sl0 = cpsw_get_slave_priv(priv, 0);
>>>
>>>           /* setup tx dma to fixed prio and zero offset */
>>> @@ -1305,10 +1306,8 @@ static int cpsw_ndo_open(struct net_device *ndev)
>>>               enable_irq(priv->irqs_table[0]);
>>>           }
>>>
>>> -        if (WARN_ON(!priv->data.rx_descs))
>>> -            priv->data.rx_descs = 128;
>>> -
>>> -        for (i = 0; i < priv->data.rx_descs; i++) {
>>> +        buf_num = cpdma_chan_get_buf_num(priv->dma) / 2;
>>
>> Could you get rid of "/ 2", pls?
>>
> Why? compiler is smart enough to translate it to shift.
> And this is not time critical place.
> Anyway, will change it to >> 1 while splitting.
> 

I mean here that cpsw, in general, should not have any knowledge about rules
 used by cpdma to split pool on rx and tx part. How about cpdma_chan_get_rx_buf_num()?

-- 
regards,
-grygorii