From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Rafał Miłecki" <zajec5@gmail.com>
Cc: "Srinivas Kandagatla" <srinivas.kandagatla@linaro.org>,
"Rafael J . Wysocki" <rafael@kernel.org>,
"Jonathan Corbet" <corbet@lwn.net>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Dan Williams" <dan.j.williams@intel.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Heiner Kallweit" <hkallweit1@gmail.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
"Rafał Miłecki" <rafal@milecki.pl>
Subject: Re: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs
Date: Tue, 21 Dec 2021 07:45:39 +0100 [thread overview]
Message-ID: <YcF4E82M89huIbSD@kroah.com> (raw)
In-Reply-To: <d68ba301-7877-a8d8-8700-c601a4996818@gmail.com>
On Tue, Dec 21, 2021 at 07:39:24AM +0100, Rafał Miłecki wrote:
> On 21.12.2021 07:33, Greg Kroah-Hartman wrote:
> > On Mon, Dec 20, 2021 at 09:39:43PM +0100, Rafał Miłecki wrote:
> > > Hi Greg,
> > >
> > > On 20.12.2021 09:00, Greg Kroah-Hartman wrote:
> > > > On Mon, Dec 20, 2021 at 07:47:30AM +0100, Rafał Miłecki wrote:
> > > > > static void nvmem_cell_entry_add(struct nvmem_cell_entry *cell)
> > > > > {
> > > > > + struct device *dev = &cell->nvmem->dev;
> > > > > + int err;
> > > > > +
> > > > > mutex_lock(&nvmem_mutex);
> > > > > list_add_tail(&cell->node, &cell->nvmem->cells);
> > > > > mutex_unlock(&nvmem_mutex);
> > > > > +
> > > > > + sysfs_attr_init(&cell->battr.attr);
> > > > > + cell->battr.attr.name = cell->name;
> > > > > + cell->battr.attr.mode = 0400;
> > > > > + cell->battr.read = nvmem_cell_attr_read;
> > > > > + err = sysfs_add_bin_file_to_group(&dev->kobj, &cell->battr,
> > > > > + nvmem_cells_group.name);
> > > >
> > > > Why not just use the is_bin_visible attribute instead to determine if
> > > > the attribute should be shown or not instead of having to add it
> > > > after-the-fact which will race with userspace and loose?
> > >
> > > I'm sorry I really don't see how you suggest to get it done.
> > >
> > > I can use .is_bin_visible() callback indeed to respect nvmem->root_only.
> >
> > Great.
> >
> > > I don't understand addig-after-the-fact part. How is .is_bin_visible()
> > > related to adding attributes for newly created cells?
> >
> > You are adding a sysfs attribute to a device that is already registered
> > in the driver core, and so the creation of that attribute is never seen
> > by userspace. The attribute needs to be attached to the device _BEFORE_
> > it is registered.
> >
> > Also, huge hint, if a driver has to call as sysfs_*() call, something is
> > wrong.
> >
> > > Do you mean I can
> > > avoid calling sysfs_add_bin_file_to_group()?
> >
> > Yes.
> >
> > > Do you recall any existing example of such solution?
> >
> > Loads.
> >
> > Just add this attribute group to your driver as a default attribute
> > group and the driver core will create it for you if needed.
> >
> > Or if you always need it, no need to mess sith is_bin_visible() at all,
> > I can't really understand what you are trying to do here at all.
>
> Thanks a lot! In nvmem_register() first there is a call to the
> device_register() and only later cells get added. I suppose I just have
> to rework nvmem_register() order so that:
> 1. Cells are collected earlier. For each cell I allocate group attribute
No, add all of the attributes to the device at the beginning before you
register it, there's no need to allocate anything.
> 2. device_register() gets called
Yes.
thanks,
greg k-h
next prev parent reply other threads:[~2021-12-21 6:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-20 6:47 [PATCH 1/2] sysfs: add sysfs_add_bin_file_to_group() Rafał Miłecki
2021-12-20 6:47 ` [PATCH 2/2] nvmem: expose NVMEM cells in sysfs Rafał Miłecki
2021-12-20 8:00 ` Greg Kroah-Hartman
2021-12-20 20:39 ` Rafał Miłecki
2021-12-21 6:33 ` Greg Kroah-Hartman
2021-12-21 6:39 ` Rafał Miłecki
2021-12-21 6:45 ` Greg Kroah-Hartman [this message]
2021-12-21 6:53 ` Rafał Miłecki
2021-12-21 7:13 ` Greg Kroah-Hartman
2021-12-21 12:24 ` Rafał Miłecki
2021-12-21 12:56 ` Greg Kroah-Hartman
2021-12-21 13:05 ` Rafał Miłecki
2021-12-21 13:27 ` Greg Kroah-Hartman
2021-12-21 13:52 ` Rafał Miłecki
2021-12-21 14:27 ` Greg Kroah-Hartman
2021-12-21 15:09 ` Rafał Miłecki
2021-12-21 15:18 ` Greg Kroah-Hartman
2021-12-21 15:33 ` Rafał Miłecki
2021-12-22 0:11 ` John Thomson
2021-12-20 8:01 ` [PATCH 1/2] sysfs: add sysfs_add_bin_file_to_group() Greg Kroah-Hartman
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