Re: [PATCH v13 4/6] nvmem: core: Rework layouts to become regular devices

Marco Felsch
2023-11-22T22:45:56Z

Hi Miquel,

sorry for answering to my own mail, I forgot something I noticed later.

On 23-11-22, Marco Felsch wrote:
> Hi Miquel,
>
> thanks a lot for your effort on this. Please see my comments inline.
>
> On 23-10-11, Miquel Raynal wrote:
> > Current layout support was initially written without modules support in
> > mind. When the requirement for module support rose, the existing base
> > was improved to adopt modularization support, but kind of a design flaw
> > was introduced. With the existing implementation, when a storage device
> > registers into NVMEM, the core tries to hook a layout (if any) and
> > populates its cells immediately. This means, if the hardware description
> > expects a layout to be hooked up, but no driver was provided for that,
> > the storage medium will fail to probe and try later from
> > scratch. Even if we consider that the hardware description shall be
> > correct, we could still probe the storage device (especially if it
> > contains the rootfs).
> >
> > One way to overcome this situation is to consider the layouts as
> > devices, and leverage the existing notifier mechanism. When a new NVMEM
> > device is registered, we can:
> > - populate its nvmem-layout child, if any
> > - try to modprobe the relevant driver, if relevant

I'm not sure why we call of_request_module() the driver framework should
handle that right?

> > - try to hook the NVMEM device with a layout in the notifier

The last part is no longer true since you don't use the notifier
anymore.

> > And when a new layout is registered:
> > - try to hook all the existing NVMEM devices which are not yet hooked to
> > a layout with the new layout
> > This way, there is no strong order to enforce, any NVMEM device creation
> > or NVMEM layout driver insertion will be observed as a new event which
> > may lead to the creation of additional cells, without disturbing the
> > probes with costly (and sometimes endless) deferrals.
> >
> > In order to achieve that goal we need:
> > * To keep track of all nvmem devices
> > * To create a new bus for the nvmem-layouts with minimal logic to match
> > nvmem-layout devices with nvmem-layout drivers.
> > All this infrastructure code is created in the layouts.c file.
> >
> > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
> > Tested-by: Rafał Miłecki <rafal@milecki.pl>

...

> > @@ -944,19 +872,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> > goto err_put_device;
> > }
> >
> > - /*
> > - * If the driver supplied a layout by config->layout, the module
> > - * pointer will be NULL and nvmem_layout_put() will be a noop.
> > - */
> > - nvmem->layout = config->layout ?: nvmem_layout_get(nvmem);
> > - if (IS_ERR(nvmem->layout)) {
> > - rval = PTR_ERR(nvmem->layout);
> > - nvmem->layout = NULL;
> > -
> > - if (rval == -EPROBE_DEFER)
> > - goto err_teardown_compat;
> > - }

Since this logic will be gone and the layout became a device the fixup
hook for the layout is more than confusing. E.g. the imx-ocotp driver
uses the layout to register a fixup for a cell which is fine but the
hook should be moved from the layout[-dev] to the config. Please see
below.

> > -
> > if (config->cells) {
> > rval = nvmem_add_cells(nvmem, config->cells, config->ncells);
> > if (rval)
> > @@ -975,7 +890,7 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> > if (rval)
> > goto err_remove_cells;
> >
> > - rval = nvmem_add_cells_from_layout(nvmem);
> > + rval = nvmem_populate_layout(nvmem);
> > if (rval)
> > goto err_remove_cells;

Also why do we populate the nvmem-layout device infront of the nvmem
device?

> >
> > @@ -983,16 +898,17 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >
> > rval = device_add(&nvmem->dev);
> > if (rval)
> > - goto err_remove_cells;
> > + goto err_destroy_layout;
> > +
> >
> > blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
> >
> > return nvmem;
> >
> > +err_destroy_layout:
> > + nvmem_destroy_layout(nvmem);
> > err_remove_cells:
> > nvmem_device_remove_all_cells(nvmem);
> > - nvmem_layout_put(nvmem->layout);
> > -err_teardown_compat:
> > if (config->compat)
> > nvmem_sysfs_remove_compat(nvmem, config);
> > err_put_device:
> > @@ -1014,7 +930,7 @@ static void nvmem_device_release(struct kref *kref)
> > device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);
> >
> > nvmem_device_remove_all_cells(nvmem);
> > - nvmem_layout_put(nvmem->layout);
> > + nvmem_destroy_layout(nvmem);
> > device_unregister(&nvmem->dev);
> > }
> >

...

> > diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
> > index 2905f9e6fc2a..a0ea8326605a 100644
> > --- a/include/linux/nvmem-provider.h
> > +++ b/include/linux/nvmem-provider.h
> > @@ -9,6 +9,7 @@
> > #ifndef _LINUX_NVMEM_PROVIDER_H
> > #define _LINUX_NVMEM_PROVIDER_H
> >
> > +#include <linux/device.h>
> > #include <linux/device/driver.h>
> > #include <linux/err.h>
> > #include <linux/errno.h>
> > @@ -154,15 +155,13 @@ struct nvmem_cell_table {
> > /**
> > * struct nvmem_layout - NVMEM layout definitions
> > *
> > - * @name: Layout name.
> > - * @of_match_table: Open firmware match table.
> > + * @dev: Device-model layout device.
> > + * @nvmem: The underlying NVMEM device
> > * @add_cells: Will be called if a nvmem device is found which
> > * has this layout. The function will add layout
> > * specific cells with nvmem_add_one_cell().
> > * @fixup_cell_info: Will be called before a cell is added. Can be
> > * used to modify the nvmem_cell_info.
> > - * @owner: Pointer to struct module.
> > - * @node: List node.
> > *
> > * A nvmem device can hold a well defined structure which can just be
> > * evaluated during runtime. For example a TLV list, or a list of "name=val"
> > @@ -170,17 +169,19 @@ struct nvmem_cell_table {
> > * cells.
> > */
> > struct nvmem_layout {
>
> Since this became a device now should we refelct this within the struct
> name, e.g. nvmem_layout_dev, nvmem_ldev, nvm_ldev?
>
> Regards,
> Marco
>
> > - const char *name;
> > - const struct of_device_id *of_match_table;
> > + struct device dev;
> > + struct nvmem_device *nvmem;
> > int (*add_cells)(struct device *dev, struct nvmem_device *nvmem,
> > struct nvmem_layout *layout);
> > void (*fixup_cell_info)(struct nvmem_device *nvmem,
> > struct nvmem_layout *layout,
> > struct nvmem_cell_info *cell);

I speak about this hook. This should be moved into the config, maybe
also renamed to fixup_dt_cell_info() or so to not confuse the users. If
we move that hook and remove the add_cells hook there are only two
members left for the cross-link.

Regards,
Marco