[mmc-next,v4,1/2] dt-bindings: mmc: document alias support

As for I2C and SPI, it now is possible to reserve a fixed index for
mmc/mmcblk devices.

Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
---

v4: moved alias documentation from example to description

v3: new patch

 Documentation/devicetree/bindings/mmc/mmc-controller.yaml | 4 ++++
 1 file changed, 4 insertions(+)

On Tue, 1 Sep 2020 at 10:50, Matthias Schiffer
<matthias.schiffer@ew.tq-group.com> wrote:
>
> As for I2C and SPI, it now is possible to reserve a fixed index for
> mmc/mmcblk devices.
>
> Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>
> v4: moved alias documentation from example to description
>
> v3: new patch
>
>  Documentation/devicetree/bindings/mmc/mmc-controller.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller.yaml
> index b96da0c7f819..f928f66fc59a 100644
> --- a/Documentation/devicetree/bindings/mmc/mmc-controller.yaml
> +++ b/Documentation/devicetree/bindings/mmc/mmc-controller.yaml
> @@ -14,6 +14,10 @@ description: |
>    that requires the respective functionality should implement them using
>    these definitions.
>
> +  It is possible to assign a fixed index mmcN to an MMC host controller
> +  (and the corresponding mmcblkN devices) by defining an alias in the
> +  /aliases device tree node.
> +
>  properties:
>    $nodename:
>      pattern: "^mmc(@.*)?$"
> --
> 2.17.1
>

On Tue, 1 Sep 2020 at 10:50, Matthias Schiffer
<matthias.schiffer@ew.tq-group.com> wrote:
>
> As with GPIO, UART and others, allow specifying the device index via the
> aliases node in the device tree.
>
> On embedded devices, there is often a combination of removable (e.g.
> SD card) and non-removable MMC devices (e.g. eMMC).
> Therefore the index might change depending on
>
> * host of removable device
> * removable card present or not
>
> This makes it difficult to hardcode the root device, if it is on the
> non-removable device. E.g. if SD card is present eMMC will be mmcblk1,
> if SD card is not present at boot, eMMC will be mmcblk0.
>
> Alternative solutions like PARTUUIDs do not cover the case where multiple
> mmcblk devices contain the same image. This is a common issue on devices
> that can boot both from eMMC (for regular boot) and SD cards (as a
> temporary boot medium for development). When a firmware image is
> installed to eMMC after a test boot via SD card, there will be no
> reliable way to refer to a specific device using (PART)UUIDs oder
> LABELs.
>
> The demand for this feature has led to multiple attempts to implement
> it, dating back at least to 2012 (see
> https://www.spinics.net/lists/linux-mmc/msg26586.html for a previous
> discussion from 2014).
>
> All indices defined in the aliases node will be reserved for use by the
> respective MMC device, moving the indices of devices that don't have an
> alias up into the non-reserved range. If the aliases node is not found,
> the driver will act as before.
>
> This is a rebased and cleaned up version of
> https://www.spinics.net/lists/linux-mmc/msg26588.html .
>
> Based-on-patch-by: Sascha Hauer <s.hauer@pengutronix.de>
> Link: https://lkml.org/lkml/2020/8/5/194
> Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>
> v4:
> - minor adjustments to commit message
>
> v3:
> - remove unneeded mmcblock changes
> - remove most helper functions to simplify code
> - extended commit message
>
> v2:
> - fix missing symbols for modular mmcblock
>
>
>
>  drivers/mmc/core/host.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/host.c b/drivers/mmc/core/host.c
> index c8fae6611b73..96b2ca1f1b06 100644
> --- a/drivers/mmc/core/host.c
> +++ b/drivers/mmc/core/host.c
> @@ -376,6 +376,20 @@ int mmc_of_parse_voltage(struct device_node *np, u32 *mask)
>  }
>  EXPORT_SYMBOL(mmc_of_parse_voltage);
>
> +/**
> + * mmc_first_nonreserved_index() - get the first index that is not reserved
> + */
> +static int mmc_first_nonreserved_index(void)
> +{
> +       int max;
> +
> +       max = of_alias_get_highest_id("mmc");
> +       if (max < 0)
> +               return 0;
> +
> +       return max + 1;
> +}
> +
>  /**
>   *     mmc_alloc_host - initialise the per-host structure.
>   *     @extra: sizeof private data structure
> @@ -387,6 +401,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
>  {
>         int err;
>         struct mmc_host *host;
> +       int alias_id, min_idx, max_idx;
>
>         host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL);
>         if (!host)
> @@ -395,7 +410,16 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
>         /* scanning will be enabled when we're ready */
>         host->rescan_disable = 1;
>
> -       err = ida_simple_get(&mmc_host_ida, 0, 0, GFP_KERNEL);
> +       alias_id = of_alias_get_id(dev->of_node, "mmc");
> +       if (alias_id >= 0) {
> +               min_idx = alias_id;
> +               max_idx = alias_id + 1;
> +       } else {
> +               min_idx = mmc_first_nonreserved_index();
> +               max_idx = 0;
> +       }
> +
> +       err = ida_simple_get(&mmc_host_ida, min_idx, max_idx, GFP_KERNEL);
>         if (err < 0) {
>                 kfree(host);
>                 return NULL;
> --
> 2.17.1
>