netdev - RE: [PATCH] net: ti: netcp: restore get/set_pad

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Date:	Tue, 9 Feb 2016 16:19:17 +0000
From:	"Karicheri, Muralidharan" <m-karicheri2@...com>
To:	David Laight <David.Laight@...LAB.COM>,
	"Strashko, Grygorii" <grygorii.strashko@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S . Miller" <davem@...emloft.net>,
	"Arnd Bergmann" <arnd@...db.de>
CC:	"Cooper Jr., Franklin" <fcooper@...com>,
	"Nori, Sekhar" <nsekhar@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Kwok, WingMan" <w-kwok2@...com>,
	"N, Mugunthan V" <mugunthanvnm@...com>
Subject: RE: [PATCH] net: ti: netcp: restore get/set_pad_info() functionality



Murali Karicheri
Linux Kernel, Software Development


>-----Original Message-----
>From: David Laight [mailto:David.Laight@...LAB.COM]
>Sent: Tuesday, February 09, 2016 11:10 AM
>To: Karicheri, Muralidharan; Strashko, Grygorii; netdev@...r.kernel.org; David S . Miller;
>Arnd Bergmann
>Cc: Cooper Jr., Franklin; Nori, Sekhar; linux-kernel@...r.kernel.org; Kwok, WingMan; N,
>Mugunthan V
>Subject: RE: [PATCH] net: ti: netcp: restore get/set_pad_info() functionality
>
>From: Karicheri, Muralidharan
>> Sent: 09 February 2016 16:10
>...
>> >In reality the 'pad' fields ought to be renamed - since they aren't pads.
>> >Perhaps they should be a union?
>
>> No. At the end of the descriptor, host software can add scratchpad
>> which is not modified by the hardware, but is used by the driver. So
>> please don't rename.
>
>So comment in the definition that the hardware doesn't modify them.
>The driver is defining these fields and they are definitely NOT padding.


It is scratch pad, not padding. Looks like pad is a confusing name. Can be
renamed to sw_data to be in sync with spec below.

The hardware spec from 
http://www.ti.com/lit/ug/sprugr9h/sprugr9h.pdf

The other SW data portion of the descriptor exists after all of the defined
words and is reserved for use by the host software to store completely
private data. This region is not used in any way by the DMA or queue manager
modules in a Multicore Navigator system and these modules will not modify
any bytes within this region.

Murali
>
>	David