linux-kernel - Re: [PATCH net-next v4 5/8] mfd: zl3073x: Add functions to work with register mailboxes

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Message-ID: <ea9cd028-3d74-4d46-b355-a74ad549269b@redhat.com>
Date: Thu, 24 Apr 2025 21:53:39 +0200
From: Ivan Vecera <ivecera@...hat.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: netdev@...r.kernel.org, Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
 Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>,
 Jiri Pirko <jiri@...nulli.us>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Prathosh Satish <Prathosh.Satish@...rochip.com>,
 Lee Jones <lee@...nel.org>, Kees Cook <kees@...nel.org>,
 Andy Shevchenko <andy@...nel.org>, Andrew Morton
 <akpm@...ux-foundation.org>, Michal Schmidt <mschmidt@...hat.com>,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH net-next v4 5/8] mfd: zl3073x: Add functions to work with
 register mailboxes



On 24. 04. 25 9:18 odp., Andrew Lunn wrote:
>> During taking 613cbb91e9ce ("media: Add MIPI CCI register access helper
>> functions") approach I found they are using for these functions u64
>> regardless of register size... Just to accommodate the biggest
>> possible value. I know about weakness of 'void *' usage but u64 is not
>> also ideal as the caller is forced to pass always 8 bytes for reading
>> and forced to reserve 8 bytes for each read value on stack.
> 
> In this device, how are the u48s used? Are they actually u48s, or are
> they just u8[6], for example a MAC address? The network stack has lots
> of functions like:
> 
> eth_hw_addr_set(struct net_device *dev, const u8 *addr)

u48 registers always represent 48bit integer... they read from device 
using bulk read as big-endian 48bit int. The same is valid also for u16
and u32.

Ivan