linux-kernel - Re: [PATCH v17 1/8] drm: bridge: Cadence: Create mhdp helper driver

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Message-ID: <2773403.mvXUDI8C0e@steina-w>
Date: Tue, 24 Sep 2024 10:41:26 +0200
From: Alexander Stein <alexander.stein@...tq-group.com>
To: dmitry.baryshkov@...aro.org, andrzej.hajda@...el.com, neil.armstrong@...aro.org, Laurent.pinchart@...asonboard.com, jonas@...boo.se, jernej.skrabec@...il.com, airlied@...il.com, daniel@...ll.ch, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, shawnguo@...nel.org, s.hauer@...gutronix.de, festevam@...il.com, vkoul@...nel.org, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org, mripard@...nel.org, Sandor Yu <Sandor.yu@....com>
Cc: kernel@...gutronix.de, linux-imx@....com, Sandor.yu@....com, oliver.brown@....com, sam@...nborg.org
Subject: Re: [PATCH v17 1/8] drm: bridge: Cadence: Create mhdp helper driver

Hi Sandor,

Am Dienstag, 24. September 2024, 09:36:46 CEST schrieb Sandor Yu:
> MHDP8546 mailbox access functions will be share to other mhdp driver
> and Cadence HDP-TX HDMI/DP PHY drivers.
> Create a new mhdp helper driver and move all those functions into.
> 
> cdns_mhdp_reg_write() is renamed to cdns_mhdp_dp_reg_write(),
> because it use the DPTX command ID DPTX_WRITE_REGISTER.
> 
> New cdns_mhdp_reg_write() is created with the general command ID
> GENERAL_REGISTER_WRITE.
> 
> Rewrite cdns_mhdp_set_firmware_active() in mhdp8546 core driver,
> use cdns_mhdp_mailbox_send() to replace cdns_mhdp_mailbox_write()
> same as the other mailbox access functions.
> 
> Replaces the local mutex mbox_mutex with a global mutex mhdp_mailbox_mutex
> to prevent race conditions in mailbox access by multi drivers.
> 
> Signed-off-by: Sandor Yu <Sandor.yu@....com>
> ---
> v16->v17:
> - Replaces the local mutex mbox_mutex with a global mutex mhdp_mailbox_mutex
> 
> v12->v16:
>  *No change.
> 
> V11->v12:
> - Move status initialize out of mbox_mutex.
> - Reorder API functions in alphabetical.
> - Add notes for malibox access functions.
> - Add year 2024 to copyright.
> 
>  drivers/gpu/drm/bridge/cadence/Kconfig        |   4 +
>  drivers/gpu/drm/bridge/cadence/Makefile       |   1 +
>  .../gpu/drm/bridge/cadence/cdns-mhdp-helper.c | 307 +++++++++++++
>  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 425 ++++--------------
>  .../drm/bridge/cadence/cdns-mhdp8546-core.h   |  47 +-
>  .../drm/bridge/cadence/cdns-mhdp8546-hdcp.c   |  36 +-
>  include/drm/bridge/cdns-mhdp-helper.h         |  94 ++++
>  7 files changed, 507 insertions(+), 407 deletions(-)
>  create mode 100644 drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
>  create mode 100644 include/drm/bridge/cdns-mhdp-helper.h
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/Kconfig b/drivers/gpu/drm/bridge/cadence/Kconfig
> index cced81633ddcd..e0973339e9e33 100644
> --- a/drivers/gpu/drm/bridge/cadence/Kconfig
> +++ b/drivers/gpu/drm/bridge/cadence/Kconfig
> @@ -21,6 +21,9 @@ config DRM_CDNS_DSI_J721E
>  	  the routing of the DSS DPI signal to the Cadence DSI.
>  endif
>  
> +config CDNS_MHDP_HELPER
> +	tristate
> +
>  config DRM_CDNS_MHDP8546
>  	tristate "Cadence DPI/DP bridge"
>  	select DRM_DISPLAY_DP_HELPER
> @@ -28,6 +31,7 @@ config DRM_CDNS_MHDP8546
>  	select DRM_DISPLAY_HELPER
>  	select DRM_KMS_HELPER
>  	select DRM_PANEL_BRIDGE
> +	select CDNS_MHDP_HELPER
>  	depends on OF
>  	help
>  	  Support Cadence DPI to DP bridge. This is an internal
> diff --git a/drivers/gpu/drm/bridge/cadence/Makefile b/drivers/gpu/drm/bridge/cadence/Makefile
> index c95fd5b81d137..087dc074820d7 100644
> --- a/drivers/gpu/drm/bridge/cadence/Makefile
> +++ b/drivers/gpu/drm/bridge/cadence/Makefile
> @@ -2,6 +2,7 @@
>  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
>  cdns-dsi-y := cdns-dsi-core.o
>  cdns-dsi-$(CONFIG_DRM_CDNS_DSI_J721E) += cdns-dsi-j721e.o
> +obj-$(CONFIG_CDNS_MHDP_HELPER) += cdns-mhdp-helper.o
>  obj-$(CONFIG_DRM_CDNS_MHDP8546) += cdns-mhdp8546.o
>  cdns-mhdp8546-y := cdns-mhdp8546-core.o cdns-mhdp8546-hdcp.o
>  cdns-mhdp8546-$(CONFIG_DRM_CDNS_MHDP8546_J721E) += cdns-mhdp8546-j721e.o
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> new file mode 100644
> index 0000000000000..c60a6b69a5343
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp-helper.c
> @@ -0,0 +1,307 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2023, 2024 NXP Semiconductor, Inc.
> + *
> + */
> +#include <drm/bridge/cdns-mhdp-helper.h>
> +#include <linux/dev_printk.h>
> +#include <linux/module.h>
> +
> +/* Protects mailbox communications with the firmware */
> +DEFINE_MUTEX(mhdp_mailbox_mutex);

This is not enough if the driver is built as a module:

> ERROR: modpost: "mhdp_mailbox_mutex"
> [drivers/gpu/drm/bridge/cadence/cdns-mhdp8546.ko] undefined! ERROR:
> modpost: "mhdp_mailbox_mutex"
> [drivers/gpu/drm/bridge/cadence/cdns-mhdp8501.ko] undefined!

Not sure if EXPORT_SYMBOL_GPL() on a mutex is considered good style.

Best regards,
Alexander

> [snip]
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