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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
drm/display: dp: implement new access helpers
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@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20250324-drm-rework-dpcd-access-v4-1-e80ff89593df@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
authored by
Dmitry Baryshkov
and committed by
Dmitry Baryshkov
d8343e11
1bb2864b
+94
-2
+4
drivers/gpu/drm/display/drm_dp_helper.c
+4
drivers/gpu/drm/display/drm_dp_helper.c
···
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* function returns -EPROTO. Errors from the underlying AUX channel transfer
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* function, with the exception of -EBUSY (which causes the transaction to
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* be retried), are propagated to the caller.
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*
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* In most of the cases you want to use drm_dp_dpcd_read_data() instead.
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*/
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ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
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void *buffer, size_t size)
···
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* function returns -EPROTO. Errors from the underlying AUX channel transfer
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* function, with the exception of -EBUSY (which causes the transaction to
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* be retried), are propagated to the caller.
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*
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* In most of the cases you want to use drm_dp_dpcd_write_data() instead.
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*/
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ssize_t drm_dp_dpcd_write(struct drm_dp_aux *aux, unsigned int offset,
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void *buffer, size_t size)
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-2
include/drm/display/drm_dp_helper.h
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-2
include/drm/display/drm_dp_helper.h
···
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void *buffer, size_t size);
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/**
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* drm_dp_dpcd_read_data() - read a series of bytes from the DPCD
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* @aux: DisplayPort AUX channel (SST or MST)
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* @offset: address of the (first) register to read
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* @buffer: buffer to store the register values
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* @size: number of bytes in @buffer
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*
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* Returns zero (0) on success, or a negative error
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* code on failure. -EIO is returned if the request was NAKed by the sink or
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* if the retry count was exceeded. If not all bytes were transferred, this
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* function returns -EPROTO. Errors from the underlying AUX channel transfer
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* function, with the exception of -EBUSY (which causes the transaction to
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* be retried), are propagated to the caller.
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*/
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static inline int drm_dp_dpcd_read_data(struct drm_dp_aux *aux,
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unsigned int offset,
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void *buffer, size_t size)
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{
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int ret;
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+
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ret = drm_dp_dpcd_read(aux, offset, buffer, size);
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if (ret < 0)
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return ret;
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if (ret < size)
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return -EPROTO;
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+
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return 0;
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}
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+
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/**
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* drm_dp_dpcd_write_data() - write a series of bytes to the DPCD
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* @aux: DisplayPort AUX channel (SST or MST)
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* @offset: address of the (first) register to write
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* @buffer: buffer containing the values to write
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* @size: number of bytes in @buffer
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*
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* Returns zero (0) on success, or a negative error
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* code on failure. -EIO is returned if the request was NAKed by the sink or
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* if the retry count was exceeded. If not all bytes were transferred, this
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* function returns -EPROTO. Errors from the underlying AUX channel transfer
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* function, with the exception of -EBUSY (which causes the transaction to
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* be retried), are propagated to the caller.
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*/
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static inline int drm_dp_dpcd_write_data(struct drm_dp_aux *aux,
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unsigned int offset,
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void *buffer, size_t size)
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{
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int ret;
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ret = drm_dp_dpcd_write(aux, offset, buffer, size);
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if (ret < 0)
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return ret;
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if (ret < size)
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return -EPROTO;
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return 0;
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}
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/**
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* drm_dp_dpcd_readb() - read a single byte from the DPCD
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* @aux: DisplayPort AUX channel
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* @offset: address of the register to read
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* @valuep: location where the value of the register will be stored
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*
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* Returns the number of bytes transferred (1) on success, or a negative
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* error code on failure.
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* error code on failure. In most of the cases you should be using
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* drm_dp_dpcd_read_byte() instead.
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*/
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static inline ssize_t drm_dp_dpcd_readb(struct drm_dp_aux *aux,
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unsigned int offset, u8 *valuep)
···
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* @value: value to write to the register
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*
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* Returns the number of bytes transferred (1) on success, or a negative
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* error code on failure.
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* error code on failure. In most of the cases you should be using
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* drm_dp_dpcd_write_byte() instead.
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*/
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static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux,
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unsigned int offset, u8 value)
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{
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return drm_dp_dpcd_write(aux, offset, &value, 1);
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}
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/**
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* drm_dp_dpcd_read_byte() - read a single byte from the DPCD
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* @aux: DisplayPort AUX channel
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* @offset: address of the register to read
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* @valuep: location where the value of the register will be stored
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*
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* Returns zero (0) on success, or a negative error code on failure.
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*/
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static inline int drm_dp_dpcd_read_byte(struct drm_dp_aux *aux,
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unsigned int offset, u8 *valuep)
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{
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return drm_dp_dpcd_read_data(aux, offset, valuep, 1);
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}
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/**
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* drm_dp_dpcd_write_byte() - write a single byte to the DPCD
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* @aux: DisplayPort AUX channel
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* @offset: address of the register to write
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* @value: value to write to the register
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*
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* Returns zero (0) on success, or a negative error code on failure.
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*/
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static inline int drm_dp_dpcd_write_byte(struct drm_dp_aux *aux,
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unsigned int offset, u8 value)
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{
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return drm_dp_dpcd_write_data(aux, offset, &value, 1);
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}
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int drm_dp_read_dpcd_caps(struct drm_dp_aux *aux,