Messages in this thread | | | Date | Tue, 21 Dec 2021 07:53:32 +0100 | Subject | Re: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs | From | Rafał Miłecki <> |
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On 21.12.2021 07:45, Greg Kroah-Hartman wrote: > 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.
If you mean static structures I can't do that, because cells almost never are static. They are not known in advance. nvmem allows cells to be: 1. Specified in OF 2. Submitted as list while registering a NVMEM device
So every cells gets its own structure allocated dynamically. My plan is to put bin_attribute in that struct and then create a group collecting all those cells.
>> 2. device_register() gets called > > Yes.
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