drm/ast: Define struct ast_ddc in ast_ddc.c

Move the definition of struct ast_ddc to ast_ddc.c and return the i2c
adapter from ast_ddc_create(). Update callers accordingly. Avoids
including Linux i2c header files, except where required. No functional
changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240403103325.30457-4-tzimmermann@suse.de

drm/ast: Group DDC init code by data structure

Reorder the code to set up the DDC channel by data structure, so
that each data structure's init is in a separate block: first the
bit algo then the i2c adapter. Makes the code more readable. No
functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240403103325.30457-3-tzimmermann@suse.de

drm/ast: Set DDC timeout in milliseconds

Compute the i2c timeout in jiffies from a value in milliseconds. The
original values of 2 jiffies equals 2 milliseconds if HZ has been
configured to a value of 1000. This corresponds to 2.2 milliseconds
used by most other DRM drivers. Update ast accordingly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 312fec1405dd ("drm: Initial KMS driver for AST (ASpeed Technologies) 2000 series (v2)")
Cc: Dave Airlie <airlied@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.5+
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240403103325.30457-2-tzimmermann@suse.de

drm/ast: Acquire I/O-register lock in DDC code

The modeset lock protects the DDC code from concurrent modeset
operations, which use the same registers. Move that code from the
connector helpers into the DDC helpers .pre_xfer() and .post_xfer().

Both, .pre_xfer() and .post_xfer(), enclose the transfer of data blocks
over the I2C channel in the internal I2C function bit_xfer(). Both
calls are executed unconditionally if present. Invoking DDC transfers
from any where within the driver now takes the lock.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-11-tzimmermann@suse.de

drm/ast: Rename struct i2c_algo_bit_data callbacks and their parameters

Align the names of the algo-bit helpers with ast's convention of
using an ast prefix plus the struct's name plus the callback's name
for such function symbols. Change the parameter names of these
helpers to 'data' and 'state', as used in the declaration of struct
i2c_algo_bit_data. No functional changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-10-tzimmermann@suse.de

drm/ast: Store AST device in struct ast_ddc

The DDC code needs the AST device. Store a pointer in struct ast_ddc
and avoid internal upcasts. Improves type safety within the DDC code.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-9-tzimmermann@suse.de

drm/ast: Pass AST device to ast_ddc_create()

The DDC code needs the AST device. Pass it to ast_ddc_create() and
avoid an internal upcast. Improves type safety within the DDC code.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-8-tzimmermann@suse.de

drm/ast: Rename struct ast_i2c_chan to struct ast_ddc

The struct struct ast_i2c_chan represents the Display Data Channel
(DDC); I2C is the underlying bus. Rename the structure, the variables
and the helper ast_i2c_create() to ddc-like terms. No functional
changes.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-7-tzimmermann@suse.de

drm/ast: Move DDC code to ast_ddc.{c,h}

Rename ast_i2c.c to ast_ddc.c and move its interface into the
new header ast_ddc.h. Update all include statements as necessary
and change the adapter name to 'AST DDC bus'.

This avoids including I2C headers in the driver's main header file,
which doesn't need them. Renaming files to _ddc indicates that the
code is about the DDC. I2C is really just the underlying bus here.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240325200855.21150-6-tzimmermann@suse.de