Re: [PATCH] net: ethernet: ax88796: initialize all fields of eeprom_93cx6 struct

[David Laight <david.laight.linux@gmail.com>]

On Fri, 24 Jul 2026 17:04:03 +0200
Stanislaw Gruszka <stf_xl@wp.pl> wrote:

> On Fri, Jul 24, 2026 at 02:57:33PM +0200, Andrew Lunn wrote:
> > On Fri, Jul 24, 2026 at 10:34:11AM +0200, stf_xl@wp.pl wrote:  
> > > From: Stanislaw Gruszka <stf_xl@wp.pl>
> > > 
> > > Commit 7738a7ab9d12 ("misc: eeprom: eeprom_93cx6: Add quirk for extra
> > > read clock cycle") added extra 'quirk' field to struct eeprom_93cx6,
> > > which change how the data is read.
> > > 
> > > Some existing users of eeprom_93cx6, including ax88796 driver, allocate
> > > the structure on the stack without initialization of all the fields.
> > > As a result, the added quirk field has undefined value, what can
> > > randomly cause reading wrong data from the EEPROM.
> > > 
> > > Fix by using designated initialization.  
> > 
> > The problem with this solution is that the next time another member is
> > added, it breaks again.  
> 
> I did not initialized 'quirks' explicitly in the patch.
> 
> > struct eeprom_93cx6 eeprom = {0};
> > 
> > Will initialise all fields to 0, and then you can use the existing
> > code to set those fields as needed.  
> 
> This form:
> 		struct eeprom_93cx6 eeprom = {
> 			.data = ei_local,
> 			.register_read = ax_eeprom_register_read,
> 			.register_write = ax_eeprom_register_write,
> 			.width = PCI_EEPROM_WIDTH_93C56,
> 		};
> 
> will also initialize _all_ remaining fields to zero.
> 
> I believe it is guaranteed by C standard.

Unless there are unions or padding...

	David

> 
> Regards
> Stanislaw
>