netdev - Re: [net-next v3 3/4] devlink: introduce flash update overwrite mask

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Date:   Wed, 19 Aug 2020 09:30:38 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Keller, Jacob E" <jacob.e.keller@...el.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [net-next v3 3/4] devlink: introduce flash update overwrite
 mask

On Wed, 19 Aug 2020 16:01:02 +0000 Keller, Jacob E wrote:
> > > -#define DEVLINK_SUPPORT_FLASH_UPDATE_COMPONENT	BIT(0)
> > > +#define DEVLINK_SUPPORT_FLASH_UPDATE_COMPONENT		BIT(0)
> > > +#define DEVLINK_SUPPORT_FLASH_UPDATE_OVERWRITE_MASK	BIT(1)  
> > 
> > Since core will check supported flags, I'd be tempted to have a flag
> > for each override type. Saves an 'if' in every driver.
> 
> Combinations might not be valid (as in ice where identifiers alone
> isn't supportable) but I suppose I could add something for it.

I see, looking at the i40e patch it does seem to not matter in practice
if core checks this or not.

> Would it make sense to just add them to the
> supported_flash_update_params? This results in a bit offset where the
> "supported" bits don't match the actual used bits in overwrite_mask,
> so we could also introduce a separate "supported_overwrite_mask" but
> that might just be overkill since I doubt we'll need to add more than
> a handlful of overwrite bits...
>
> > >  struct devlink_region;
> > >  struct devlink_info_req;
> > > diff --git a/include/uapi/linux/devlink.h
> > > b/include/uapi/linux/devlink.h index cfef4245ea5a..1d8bbe9c1ae1
> > > 100644 --- a/include/uapi/linux/devlink.h
> > > +++ b/include/uapi/linux/devlink.h
> > > @@ -228,6 +228,28 @@ enum {
> > >  	DEVLINK_ATTR_STATS_MAX = __DEVLINK_ATTR_STATS_MAX - 1
> > >  };
> > >
> > > +/* Specify what sections of a flash component can be overwritten
> > > when
> > > + * performing an update. Overwriting of firmware binary sections
> > > is always
> > > + * implicitly assumed to be allowed.
> > > + *
> > > + * Each section must be documented in
> > > + * Documentation/networking/devlink/devlink-flash.rst
> > > + *
> > > + */
> > > +enum {
> > > +	DEVLINK_FLASH_OVERWRITE_SETTINGS_BIT,
> > > +	DEVLINK_FLASH_OVERWRITE_IDENTIFIERS_BIT,  
> > 
> > IMHO generally a good practice to have 0 be undefined.
> 
> Even for bits? I saw that for attribute values 0 was undefined, but
> that didn't seem right for a bit position. sending the bitfield with
> zero bit set means the same as not sending the bitfield.

Ah, misread the code, sorry.