Re: [PATCH v4 1/6] drm: Add SCDC helpers

Ville Syrjälä
2017-02-23T11:41:42Z

On Thu, Feb 23, 2017 at 08:51:03AM +0530, Sharma, Shashank wrote:
> Thanks for the review Ville, my comments inline.
>
> Regards
>
> Shashank
>
>
> On 2/22/2017 10:39 PM, Ville Syrjälä wrote:
> > On Wed, Feb 22, 2017 at 06:48:26PM +0530, Shashank Sharma wrote:
> >> From: Thierry Reding <treding@nvidia.com>
> >>
> >> SCDC is a mechanism defined in the HDMI 2.0 specification that allows
> >> the source and sink devices to communicate.
> >>
> >> This commit introduces helpers to access the SCDC and provides the
> >> symbolic names for the various registers defined in the specification.
> >>
> >> V2: Rebase.
> >> V3: Added R-B from Jose.
> >> V4: Rebase
> >>
> >> Signed-off-by: Thierry Reding <treding@nvidia.com>
> >> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> >> Reviewed-by: Jose Abreu <joabreu@synopsys.com>
> >> ---
> >> Documentation/gpu/drm-kms-helpers.rst | 12 ++++
> >> drivers/gpu/drm/Makefile | 3 +-
> >> drivers/gpu/drm/drm_scdc_helper.c | 111 ++++++++++++++++++++++++++++
> >> include/drm/drm_scdc_helper.h | 132 ++++++++++++++++++++++++++++++++++
> >> 4 files changed, 257 insertions(+), 1 deletion(-)
> >> create mode 100644 drivers/gpu/drm/drm_scdc_helper.c
> >> create mode 100644 include/drm/drm_scdc_helper.h
> >>
> >> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst
> >> index 03040aa..7592756 100644
> >> --- a/Documentation/gpu/drm-kms-helpers.rst
> >> +++ b/Documentation/gpu/drm-kms-helpers.rst
> >> @@ -217,6 +217,18 @@ EDID Helper Functions Reference
> >> .. kernel-doc:: drivers/gpu/drm/drm_edid.c
> >> :export:
> >>
> >> +SCDC Helper Functions Reference
> >> +===============================
> >> +
> >> +.. kernel-doc:: drivers/gpu/drm/drm_scdc_helper.c
> >> + :doc: scdc helpers
> >> +
> >> +.. kernel-doc:: include/drm/drm_scdc_helper.h
> >> + :internal:
> >> +
> >> +.. kernel-doc:: drivers/gpu/drm/drm_scdc_helper.c
> >> + :export:
> >> +
> >> Rectangle Utilities Reference
> >> =============================
> >>
> >> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> >> index 92de399..ad91cd9 100644
> >> --- a/drivers/gpu/drm/Makefile
> >> +++ b/drivers/gpu/drm/Makefile
> >> @@ -31,7 +31,8 @@ drm-$(CONFIG_DEBUG_FS) += drm_debugfs.o drm_debugfs_crc.o
> >> drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
> >> drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
> >> drm_kms_helper_common.o drm_dp_dual_mode_helper.o \
> >> - drm_simple_kms_helper.o drm_modeset_helper.o
> >> + drm_simple_kms_helper.o drm_modeset_helper.o \
> >> + drm_scdc_helper.o
> >>
> >> drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> >> drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> >> diff --git a/drivers/gpu/drm/drm_scdc_helper.c b/drivers/gpu/drm/drm_scdc_helper.c
> >> new file mode 100644
> >> index 0000000..fe0e121
> >> --- /dev/null
> >> +++ b/drivers/gpu/drm/drm_scdc_helper.c
> >> @@ -0,0 +1,111 @@
> >> +/*
> >> + * Copyright (c) 2015 NVIDIA Corporation. All rights reserved.
> >> + *
> >> + * Permission is hereby granted, free of charge, to any person obtaining a
> >> + * copy of this software and associated documentation files (the "Software"),
> >> + * to deal in the Software without restriction, including without limitation
> >> + * the rights to use, copy, modify, merge, publish, distribute, sub license,
> >> + * and/or sell copies of the Software, and to permit persons to whom the
> >> + * Software is furnished to do so, subject to the following conditions:
> >> + *
> >> + * The above copyright notice and this permission notice (including the
> >> + * next paragraph) shall be included in all copies or substantial portions
> >> + * of the Software.
> >> + *
> >> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> >> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> >> + * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
> >> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> >> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> >> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> >> + * DEALINGS IN THE SOFTWARE.
> >> + */
> >> +
> >> +#include <linux/slab.h>
> >> +
> >> +#include <drm/drm_scdc_helper.h>
> >> +
> >> +/**
> >> + * DOC: scdc helpers
> >> + *
> >> + * Status and Control Data Channel (SCDC) is a mechanism introduced by the
> >> + * HDMI 2.0 specification. It is a point-to-point protocol that allows the
> >> + * HDMI source and HDMI sink to exchange data. The same I2C interface that
> >> + * is used to access EDID serves as the transport mechanism for SCDC.
> >> + */
> >> +
> >> +#define SCDC_I2C_SLAVE_ADDRESS 0x54
> >> +
> >> +/**
> >> + * drm_scdc_read - read a block of data from SCDC
> >> + * @adapter: I2C controller
> >> + * @offset: start offset of block to read
> >> + * @buffer: return location for the block to read
> >> + * @size: size of the block to read
> >> + *
> >> + * Reads a block of data from SCDC, starting at a given offset.
> >> + *
> >> + * Returns:
> >> + * The number of bytes read from SCDC or a negative error code on failure.
> >> + */
> >> +ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
> >> + size_t size)
> >> +{
> >> + struct i2c_msg msgs[2] = {
> >> + {
> >> + .addr = SCDC_I2C_SLAVE_ADDRESS,
> >> + .flags = 0,
> >> + .len = 1,
> >> + .buf = &offset,
> >> + }, {
> >> + .addr = SCDC_I2C_SLAVE_ADDRESS,
> >> + .flags = I2C_M_RD,
> >> + .len = size,
> >> + .buf = buffer,
> >> + }
> >> + };
> >> +
> >> + return i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
> > That still disagrees with the documentation. I would suggest doing what
> > the DP dual mode helper does.
> Sure, I guess this is about how we are handling the return values from
> I2C layer, I will change it
> the way its handled in drm_dp_dual_mode functions
> >
> >> +}
> >> +EXPORT_SYMBOL(drm_scdc_read);
> >> +
> >> +/**
> >> + * drm_scdc_write - write a block of data to SCDC
> >> + * @adapter: I2C controller
> >> + * @offset: start offset of block to write
> >> + * @buffer: block of data to write
> >> + * @size: size of the block to write
> >> + *
> >> + * Writes a block of data to SCDC, starting at a given offset.
> >> + *
> >> + * Returns:
> >> + * The number of bytes written to SCDC or a negative error code on failure.
> >> + */
> >> +ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
> >> + const void *buffer, size_t size)
> >> +{
> >> + struct i2c_msg msg = {
> >> + .addr = SCDC_I2C_SLAVE_ADDRESS,
> >> + .flags = 0,
> >> + .len = 1 + size,
> >> + .buf = NULL,
> >> + };
> >> + void *data;
> >> + int err;
> >> +
> >> + data = kmalloc(1 + size, GFP_TEMPORARY);
> >> + if (!data)
> >> + return -ENOMEM;
> >> +
> >> + msg.buf = data;
> >> +
> >> + memcpy(data, &offset, sizeof(offset));
> >> + memcpy(data + 1, buffer, size);
> >> +
> >> + err = i2c_transfer(adapter, &msg, 1);
> >> +
> >> + kfree(data);
> >> +
> >> + return err;
> >> +}
> >> +EXPORT_SYMBOL(drm_scdc_write);
> >> diff --git a/include/drm/drm_scdc_helper.h b/include/drm/drm_scdc_helper.h
> >> new file mode 100644
> >> index 0000000..93b07bc
> >> --- /dev/null
> >> +++ b/include/drm/drm_scdc_helper.h
> >> @@ -0,0 +1,132 @@
> >> +/*
> >> + * Copyright (c) 2015 NVIDIA Corporation. All rights reserved.
> >> + *
> >> + * Permission is hereby granted, free of charge, to any person obtaining a
> >> + * copy of this software and associated documentation files (the "Software"),
> >> + * to deal in the Software without restriction, including without limitation
> >> + * the rights to use, copy, modify, merge, publish, distribute, sub license,
> >> + * and/or sell copies of the Software, and to permit persons to whom the
> >> + * Software is furnished to do so, subject to the following conditions:
> >> + *
> >> + * The above copyright notice and this permission notice (including the
> >> + * next paragraph) shall be included in all copies or substantial portions
> >> + * of the Software.
> >> + *
> >> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> >> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> >> + * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
> >> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> >> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> >> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> >> + * DEALINGS IN THE SOFTWARE.
> >> + */
> >> +
> >> +#ifndef DRM_SCDC_HELPER_H
> >> +#define DRM_SCDC_HELPER_H
> >> +
> >> +#include <linux/i2c.h>
> >> +#include <linux/types.h>
> >> +
> >> +#define SCDC_SINK_VERSION 0x01
> >> +
> >> +#define SCDC_SOURCE_VERSION 0x02
> >> +
> >> +#define SCDC_UPDATE_0 0x10
> >> +#define SCDC_READ_REQUEST_TEST (1 << 2)
> >> +#define SCDC_CED_UPDATE (1 << 1)
> >> +#define SCDC_STATUS_UPDATE (1 << 0)
> >> +
> >> +#define SCDC_UPDATE_1 0x11
> >> +
> >> +#define SCDC_TMDS_CONFIG 0x20
> >> +#define SCDC_TMDS_BIT_CLOCK_RATIO_BY_40 (1 << 1)
> >> +#define SCDC_TMDS_BIT_CLOCK_RATIO_BY_10 (0 << 1)
> >> +#define SCDC_SCRAMBLING_ENABLE (1 << 0)
> >> +
> >> +#define SCDC_SCRAMBLER_STATUS 0x21
> >> +#define SCDC_SCRAMBLING_STATUS (1 << 0)
> >> +
> >> +#define SCDC_CONFIG_0 0x30
> >> +#define SCDC_READ_REQUEST_ENABLE (1 << 0)
> >> +
> >> +#define SCDC_STATUS_FLAGS_0 0x40
> >> +#define SCDC_CH2_LOCK (1 < 3)
> >> +#define SCDC_CH1_LOCK (1 < 2)
> >> +#define SCDC_CH0_LOCK (1 < 1)
> >> +#define SCDC_CH_LOCK_MASK (SCDC_CH2_LOCK | SCDC_CH1_LOCK | SCDC_CH0_LOCK)
> >> +#define SCDC_CLOCK_DETECT (1 << 0)
> >> +
> >> +#define SCDC_STATUS_FLAGS_1 0x41
> >> +
> >> +#define SCDC_ERR_DET_0_L 0x50
> >> +#define SCDC_ERR_DET_0_H 0x51
> >> +#define SCDC_ERR_DET_1_L 0x52
> >> +#define SCDC_ERR_DET_1_H 0x53
> >> +#define SCDC_ERR_DET_2_L 0x54
> >> +#define SCDC_ERR_DET_2_H 0x55
> >> +#define SCDC_CHANNEL_VALID (1 << 7)
> >> +
> >> +#define SCDC_ERR_DET_CHECKSUM 0x56
> >> +
> >> +#define SCDC_TEST_CONFIG_0 0xc0
> >> +#define SCDC_TEST_READ_REQUEST (1 << 7)
> >> +#define SCDC_TEST_READ_REQUEST_DELAY(x) ((x) & 0x7f)
> >> +
> >> +#define SCDC_MANUFACTURER_IEEE_OUI 0xd0
> >> +#define SCDC_MANUFACTURER_IEEE_OUI_SIZE 3
> >> +
> >> +#define SCDC_DEVICE_ID 0xd3
> >> +#define SCDC_DEVICE_ID_SIZE 8
> >> +
> >> +#define SCDC_DEVICE_HARDWARE_REVISION 0xdb
> >> +#define SCDC_DEVICE_HARDWARE_REVISION_MAJOR(x) (((x) >> 4) & 0xf)
> >> +#define SCDC_DEVICE_HARDWARE_REVISION_MINOR(x) (((x) >> 0) & 0xf)
> > We don't usually define macros like this to extract information from the
> > register. It's easy to confuse them with the normal macros for setting
> > bits.
> How about if I add another sub macro called _MAJOR, and use it like this:
>
> #define _MAJOR(x) (x & 0xf)
> #define SCDC_DEVICE_HARDWARE_REVISION_MAJOR(x) (_MAJOR((x) >> 4))
>
> Or will you prefer no macro for this job at all ?

I think the usual pattern is a SHIFT + MASK macros for extracting
things from register values. But that is a little error prone and rather
verbose to use, so I do actually like the idea of having macros for
extracting bits from registers.

Hmm. After looking around a bit, I do see that DP_GET_SINK_COUNT() is an
extraction macro similar to what you have here. If we follow that example
then just adding _GET_ to the name should be good enough to distinguish
this from any macro to set the bits.

>
> - Shashank
> >> +
> >> +#define SCDC_DEVICE_SOFTWARE_MAJOR_REVISION 0xdc
> >> +#define SCDC_DEVICE_SOFTWARE_MINOR_REVISION 0xdd
> >> +
> >> +#define SCDC_MANUFACTURER_SPECIFIC 0xde
> >> +#define SCDC_MANUFACTURER_SPECIFIC_SIZE 34
> >> +
> >> +ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
> >> + size_t size);
> >> +ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
> >> + const void *buffer, size_t size);
> >> +
> >> +/**
> >> + * drm_scdc_readb - read a single byte from SCDC
> >> + * @adapter: I2C adapter
> >> + * @offset: offset of register to read
> >> + * @value: return location for the register value
> >> + *
> >> + * Reads a single byte from SCDC. This is a convenience wrapper around the
> >> + * drm_scdc_read() function.
> >> + *
> >> + * Returns:
> >> + * 0 on success or a negative error code on failure.
> >> + */
> >> +static inline int drm_scdc_readb(struct i2c_adapter *adapter, u8 offset,
> >> + u8 *value)
> >> +{
> >> + return drm_scdc_read(adapter, offset, value, sizeof(*value));
> >> +}
> >> +
> >> +/**
> >> + * drm_scdc_writeb - write a single byte to SCDC
> >> + * @adapter: I2C adapter
> >> + * @offset: offset of register to read
> >> + * @value: return location for the register value
> >> + *
> >> + * Writes a single byte to SCDC. This is a convenience wrapper around the
> >> + * drm_scdc_write() function.
> >> + *
> >> + * Returns:
> >> + * 0 on success or a negative error code on failure.
> >> + */
> >> +static inline int drm_scdc_writeb(struct i2c_adapter *adapter, u8 offset,
> >> + u8 value)
> >> +{
> >> + return drm_scdc_write(adapter, offset, &value, sizeof(value));
> >> +}
> >> +
> >> +#endif
> >> --
> >> 1.9.1

--
Ville Syrjälä
Intel OTC
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