linux-kernel - Re: [PATCH v4 15/19] fpga: dfl: convert is_feature_dev

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Message-ID: <ZzvnkPzZ7FBPgonr@yilunxu-OptiPlex-7050>
Date: Tue, 19 Nov 2024 09:19:12 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: "Colberg, Peter" <peter.colberg@...el.com>
Cc: "Xu, Yilun" <yilun.xu@...el.com>,
	"linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
	"mdf@...nel.org" <mdf@...nel.org>, "Wu, Hao" <hao.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"russ.weight@...ux.dev" <russ.weight@...ux.dev>,
	"Pagani, Marco" <marpagan@...hat.com>,
	"trix@...hat.com" <trix@...hat.com>,
	"basheer.ahmed.muddebihal@...ux.intel.com" <basheer.ahmed.muddebihal@...ux.intel.com>,
	"matthew.gerlach@...ux.intel.com" <matthew.gerlach@...ux.intel.com>
Subject: Re: [PATCH v4 15/19] fpga: dfl: convert is_feature_dev_detected() to
 use FIU type

On Mon, Nov 18, 2024 at 11:00:28PM +0000, Colberg, Peter wrote:
> On Mon, 2024-11-18 at 22:32 +0800, Xu Yilun wrote:
> > On Fri, Oct 25, 2024 at 06:37:10PM -0400, Peter Colberg wrote:
> > > Use binfo->type instead of binfo->feature_dev to decide whether a
> > > feature device was detected during feature parsing. A subsequent
> > > commit will delay the allocation of the feature platform device
> > > to feature_dev_register() and remove binfo->feature_dev.
> > > 
> > > This commit does not introduce any functional changes.
> > > 
> > > Signed-off-by: Peter Colberg <peter.colberg@...el.com>
> > > Reviewed-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> > > Reviewed-by: Basheer Ahmed Muddebihal <basheer.ahmed.muddebihal@...ux.intel.com>
> > > ---
> > > Changes since v3:
> > > - New patch extracted from last patch of v3 series.
> > > ---
> > >  drivers/fpga/dfl.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
> > > index 758673b0290a..a9ec37278b2d 100644
> > > --- a/drivers/fpga/dfl.c
> > > +++ b/drivers/fpga/dfl.c
> > > @@ -1248,7 +1248,7 @@ static int parse_feature_port_afu(struct build_feature_devs_info *binfo,
> > >  return create_feature_instance(binfo, ofst, size, FEATURE_ID_AFU);
> > >  }
> > >  
> > > -#define is_feature_dev_detected(binfo) (!!(binfo)->feature_dev)
> > > +#define is_feature_dev_detected(binfo) ((binfo)->type != DFL_ID_MAX)
> > 
> > I still doesn't get why put the change here. How it resolves my concern
> > compared to v3?
> 
> Could you elaborate on your concern? I moved this change into a
> separate commit so that it is not lost in other changes, but I don't

I did't mean this change had to be separated, I doubt it impacts the
functionality when it was applied. After the series were all applied the
issue may be fixed but people review patches one by one.

> see how the two definitions would not be functionally equivalent. Would
> it help to extend the commit description along the following lines?
> 
>    1. Before this series, binfo->feature_dev was initialized to NULL by
>       devm_kzalloc() in dfl_fpga_feature_devs_enumerate(). After this
>       series, binfo->type is initialized to DFL_ID_MAX in
>       dfl_fpga_feature_devs_enumerate().
>    2. Before this series, binfo->feature_dev was set to a non-NULL
>       pointer in build_info_create_dev(), which in turn was called from

So at the point of *this patch* is applied, binfo->feature_dev & binfo->type
don't initialize at the same time, there is some gap the caller of
is_feature_dev_detected() would get a different result, e.g.
when build_info_create_dev() fails, binfo->type holds valid DFL_ID but
binfo->feature_dev is NULL.

>       parse_feature_fiu(). After this series, binfo->type is set to a
>       non-DFL_ID_MAX value, as returned by dfh_id_to_type(), in
>       parse_feature_fiu().
>    3. Before this series, binfo->feature_dev was reset to NULL at the
>       end of build_info_commit_dev(). After this series, binfo->type is
>       reset to DFL_ID_MAX at the end of build_info_commit_dev().
> 
> Thanks,
> Peter
> 
> > 
> > Thanks,
> > Yilun
> > 
> > >  
> > >  static int parse_feature_afu(struct build_feature_devs_info *binfo,
> > >  resource_size_t ofst)
> > > -- 
> > > 2.47.0
> > > 
> > > 
>