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Message-Id: <20250307-drm-rework-dpcd-access-v3-1-9044a3a868ee@linaro.org>
Date: Fri, 07 Mar 2025 06:34:43 +0200
From: Dmitry Baryshkov <lumag@...nel.org>
To: Lyude Paul <lyude@...hat.com>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Rob Clark <robdclark@...il.com>, Abhinav Kumar <quic_abhinavk@...cinc.com>,
Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>,
Jani Nikula <jani.nikula@...ux.intel.com>,
Alex Deucher <alexander.deucher@....com>,
Christian König <christian.koenig@....com>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
Xinliang Liu <xinliang.liu@...aro.org>, Tian Tao <tiantao6@...ilicon.com>,
Xinwei Kong <kong.kongxinwei@...ilicon.com>,
Sumit Semwal <sumit.semwal@...aro.org>,
Yongqin Liu <yongqin.liu@...aro.org>, John Stultz <jstultz@...gle.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
amd-gfx@...ts.freedesktop.org, Jani Nikula <jani.nikula@...el.com>
Subject: [PATCH RFC v3 1/7] drm/display: dp: implement new access helpers
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Existing DPCD access functions return an error code or the number of
bytes being read / write in case of partial access. However a lot of
drivers either (incorrectly) ignore partial access or mishandle error
codes. In other cases this results in a boilerplate code which compares
returned value with the size.
Implement new set of DPCD access helpers, which ignore partial access,
always return 0 or an error code.
Suggested-by: Jani Nikula <jani.nikula@...ux.intel.com>
Acked-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
---
drivers/gpu/drm/display/drm_dp_helper.c | 4 ++
include/drm/display/drm_dp_helper.h | 92 ++++++++++++++++++++++++++++++++-
2 files changed, 94 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index dbce1c3f49691fc687fee2404b723c73d533f23d..e43a8f4a252dae22eeaae1f4ca94da064303033d 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -704,6 +704,8 @@ EXPORT_SYMBOL(drm_dp_dpcd_set_powered);
* function returns -EPROTO. Errors from the underlying AUX channel transfer
* function, with the exception of -EBUSY (which causes the transaction to
* be retried), are propagated to the caller.
+ *
+ * In most of the cases you want to use drm_dp_dpcd_read_data() instead.
*/
ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
void *buffer, size_t size)
@@ -752,6 +754,8 @@ EXPORT_SYMBOL(drm_dp_dpcd_read);
* function returns -EPROTO. Errors from the underlying AUX channel transfer
* function, with the exception of -EBUSY (which causes the transaction to
* be retried), are propagated to the caller.
+ *
+ * In most of the cases you want to use drm_dp_dpcd_write_data() instead.
*/
ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
void *buffer, size_t size)
diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
index 5ae4241959f24e2c1fb581d7c7d770485d603099..c5be44d72c9a04474f6c795e03bf02bf08f5eaef 100644
--- a/include/drm/display/drm_dp_helper.h
+++ b/include/drm/display/drm_dp_helper.h
@@ -527,6 +527,64 @@ ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
void *buffer, size_t size);
+/**
+ * drm_dp_dpcd_read_data() - read a series of bytes from the DPCD
+ * @aux: DisplayPort AUX channel (SST or MST)
+ * @offset: address of the (first) register to read
+ * @buffer: buffer to store the register values
+ * @size: number of bytes in @buffer
+ *
+ * Returns zero (0) on success, or a negative error
+ * code on failure. -EIO is returned if the request was NAKed by the sink or
+ * if the retry count was exceeded. If not all bytes were transferred, this
+ * function returns -EPROTO. Errors from the underlying AUX channel transfer
+ * function, with the exception of -EBUSY (which causes the transaction to
+ * be retried), are propagated to the caller.
+ */
+static inline int drm_dp_dpcd_read_data(struct drm_dp_aux *aux,
+ unsigned int offset,
+ void *buffer, size_t size)
+{
+ int ret;
+
+ ret = drm_dp_dpcd_read(aux, offset, buffer, size);
+ if (ret < 0)
+ return ret;
+ if (ret < size)
+ return -EPROTO;
+
+ return 0;
+}
+
+/**
+ * drm_dp_dpcd_write_data() - write a series of bytes to the DPCD
+ * @aux: DisplayPort AUX channel (SST or MST)
+ * @offset: address of the (first) register to write
+ * @buffer: buffer containing the values to write
+ * @size: number of bytes in @buffer
+ *
+ * Returns zero (0) on success, or a negative error
+ * code on failure. -EIO is returned if the request was NAKed by the sink or
+ * if the retry count was exceeded. If not all bytes were transferred, this
+ * function returns -EPROTO. Errors from the underlying AUX channel transfer
+ * function, with the exception of -EBUSY (which causes the transaction to
+ * be retried), are propagated to the caller.
+ */
+static inline int drm_dp_dpcd_write_data(struct drm_dp_aux *aux,
+ unsigned int offset,
+ void *buffer, size_t size)
+{
+ int ret;
+
+ ret = drm_dp_dpcd_write(aux, offset, buffer, size);
+ if (ret < 0)
+ return ret;
+ if (ret < size)
+ return -EPROTO;
+
+ return 0;
+}
+
/**
* drm_dp_dpcd_readb() - read a single byte from the DPCD
* @aux: DisplayPort AUX channel
@@ -534,7 +592,8 @@ ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
* @valuep: location where the value of the register will be stored
*
* Returns the number of bytes transferred (1) on success, or a negative
- * error code on failure.
+ * error code on failure. In most of the cases you should be using
+ * drm_dp_dpcd_read_byte() instead
*/
static inline ssize_t drm_dp_dpcd_readb(struct drm_dp_aux *aux,
unsigned int offset, u8 *valuep)
@@ -549,7 +608,8 @@ static inline ssize_t drm_dp_dpcd_readb(struct drm_dp_aux *aux,
* @value: value to write to the register
*
* Returns the number of bytes transferred (1) on success, or a negative
- * error code on failure.
+ * error code on failure. In most of the cases you should be using
+ * drm_dp_dpcd_write_byte() instead
*/
static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
unsigned int offset, u8 value)
@@ -557,6 +617,34 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
return drm_dp_dpcd_write(aux, offset, &value, 1);
}
+/**
+ * drm_dp_dpcd_read_byte() - read a single byte from the DPCD
+ * @aux: DisplayPort AUX channel
+ * @offset: address of the register to read
+ * @valuep: location where the value of the register will be stored
+ *
+ * Returns zero (0) on success, or a negative error code on failure.
+ */
+static inline int drm_dp_dpcd_read_byte(struct drm_dp_aux *aux,
+ unsigned int offset, u8 *valuep)
+{
+ return drm_dp_dpcd_read_data(aux, offset, valuep, 1);
+}
+
+/**
+ * drm_dp_dpcd_write_byte() - write a single byte to the DPCD
+ * @aux: DisplayPort AUX channel
+ * @offset: address of the register to write
+ * @value: value to write to the register
+ *
+ * Returns zero (0) on success, or a negative error code on failure.
+ */
+static inline int drm_dp_dpcd_write_byte(struct drm_dp_aux *aux,
+ unsigned int offset, u8 value)
+{
+ return drm_dp_dpcd_write_data(aux, offset, &value, 1);
+}
+
int drm_dp_read_dpcd_caps(struct drm_dp_aux *aux,
u8 dpcd[DP_RECEIVER_CAP_SIZE]);
--
2.39.5
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