linux-kernel - Re: [PATCH net-next 07/15] net: macb: simplify macb_adj_dma_desc

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Message-Id: <DDN4RIQJDP38.DTL27ATUDSYA@bootlin.com>
Date: Mon, 20 Oct 2025 13:58:49 +0200
From: Théo Lebrun <theo.lebrun@...tlin.com>
To: "Andrew Lunn" <andrew@...n.ch>, Théo Lebrun
 <theo.lebrun@...tlin.com>
Cc: "Andrew Lunn" <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>, "Rob
 Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>, "Nicolas Ferre"
 <nicolas.ferre@...rochip.com>, "Claudiu Beznea" <claudiu.beznea@...on.dev>,
 "Richard Cochran" <richardcochran@...il.com>, "Russell King"
 <linux@...linux.org.uk>, <netdev@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Vladimir
 Kondratiev" <vladimir.kondratiev@...ileye.com>, "Tawfik Bayouk"
 <tawfik.bayouk@...ileye.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>, Grégory Clement
 <gregory.clement@...tlin.com>, Benoît Monin
 <benoit.monin@...tlin.com>, "Maxime Chevallier"
 <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next 07/15] net: macb: simplify
 macb_adj_dma_desc_idx()

Hello Andrew,

On Fri Oct 17, 2025 at 8:00 PM CEST, Andrew Lunn wrote:
> On Tue, Oct 14, 2025 at 05:25:08PM +0200, Théo Lebrun wrote:
>> The function body uses a switch statement on bp->hw_dma_cap and handles
>> its four possible values: 0, is_64b, is_ptp, is_64b && is_ptp.
>> 
>> Instead, refactor by noticing that the return value is:
>>    desc_size * MULT
>> with MULT = 3 if is_64b && is_ptp,
>>             2 if is_64b || is_ptp,
>>             1 otherwise.
>> 
>> MULT can be expressed as:
>>    1 + is_64b + is_ptp
>> 
>> Signed-off-by: Théo Lebrun <theo.lebrun@...tlin.com>
>> ---
>>  drivers/net/ethernet/cadence/macb_main.c | 18 ++++++------------
>>  1 file changed, 6 insertions(+), 12 deletions(-)
>> 
>> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
>> index 7f74e280a3351ee7f961ff5ecd9550470b2e68eb..44a411662786ca4f309d6f9389b0d36819fc40ad 100644
>> --- a/drivers/net/ethernet/cadence/macb_main.c
>> +++ b/drivers/net/ethernet/cadence/macb_main.c
>> @@ -136,19 +136,13 @@ static unsigned int macb_dma_desc_get_size(struct macb *bp)
>>  static unsigned int macb_adj_dma_desc_idx(struct macb *bp, unsigned int desc_idx)
>>  {
>>  #ifdef MACB_EXT_DESC
>> -	switch (bp->hw_dma_cap) {
>> -	case HW_DMA_CAP_64B:
>> -	case HW_DMA_CAP_PTP:
>> -		desc_idx <<= 1;
>> -		break;
>> -	case HW_DMA_CAP_64B_PTP:
>
> I _think_ this makes HW_DMA_CAP_64B_PTP unused and it can be removed?

It does indeed. That constant gets removed in the following patch
([08/15], "net: macb: move bp->hw_dma_cap flags to bp->caps").
It  appeared to make more sense to remove all HW_DMA_CAP_* at once.
You probably noticed as you continued your review.

Thanks for the review! I guess you have spotted that the series got
applied to netdev/net-next by Jakub [0].

[0]: https://lore.kernel.org/lkml/176066582948.1978978.752807229943547484.git-patchwork-notify@kernel.org/

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com