sys/dev/drm/drm_scdc_helper.c

   1 /*
   2  * Copyright (c) 2015 NVIDIA Corporation. All rights reserved.
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sub license,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the
  12  * next paragraph) shall be included in all copies or substantial portions
  13  * of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 #include <linux/slab.h>
  25 #include <linux/delay.h>
  26
  27 #include <drm/drm_scdc_helper.h>
  28 #include <drm/drmP.h>
  29
  30 /**
  31  * DOC: scdc helpers
  32  *
  33  * Status and Control Data Channel (SCDC) is a mechanism introduced by the
  34  * HDMI 2.0 specification. It is a point-to-point protocol that allows the
  35  * HDMI source and HDMI sink to exchange data. The same I2C interface that
  36  * is used to access EDID serves as the transport mechanism for SCDC.
  37  */
  38
  39 #define SCDC_I2C_SLAVE_ADDRESS 0x54
  40
  41 /**
  42  * drm_scdc_read - read a block of data from SCDC
  43  * @adapter: I2C controller
  44  * @offset: start offset of block to read
  45  * @buffer: return location for the block to read
  46  * @size: size of the block to read
  47  *
  48  * Reads a block of data from SCDC, starting at a given offset.
  49  *
  50  * Returns:
  51  * 0 on success, negative error code on failure.
  52  */
  53 ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
  54                       size_t size)
  55 {
  56         int ret;
  57         struct i2c_msg msgs[2] = {
  58                 {
  59                         .addr = SCDC_I2C_SLAVE_ADDRESS,
  60                         .flags = 0,
  61                         .len = 1,
  62                         .buf = &offset,
  63                 }, {
  64                         .addr = SCDC_I2C_SLAVE_ADDRESS,
  65                         .flags = I2C_M_RD,
  66                         .len = size,
  67                         .buf = buffer,
  68                 }
  69         };
  70
  71         ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
  72         if (ret < 0)
  73                 return ret;
  74         if (ret != ARRAY_SIZE(msgs))
  75                 return -EPROTO;
  76
  77         return 0;
  78 }
  79 EXPORT_SYMBOL(drm_scdc_read);
  80
  81 /**
  82  * drm_scdc_write - write a block of data to SCDC
  83  * @adapter: I2C controller
  84  * @offset: start offset of block to write
  85  * @buffer: block of data to write
  86  * @size: size of the block to write
  87  *
  88  * Writes a block of data to SCDC, starting at a given offset.
  89  *
  90  * Returns:
  91  * 0 on success, negative error code on failure.
  92  */
  93 ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
  94                        const void *buffer, size_t size)
  95 {
  96         struct i2c_msg msg = {
  97                 .addr = SCDC_I2C_SLAVE_ADDRESS,
  98                 .flags = 0,
  99                 .len = 1 + size,
 100                 .buf = NULL,
 101         };
 102         void *data;
 103         int err;
 104
 105         data = kmalloc(1 + size, M_DRM, GFP_KERNEL);
 106         if (!data)
 107                 return -ENOMEM;
 108
 109         msg.buf = data;
 110
 111         memcpy(data, &offset, sizeof(offset));
 112         memcpy(data + 1, buffer, size);
 113
 114         err = i2c_transfer(adapter, &msg, 1);
 115
 116         kfree(data);
 117
 118         if (err < 0)
 119                 return err;
 120         if (err != 1)
 121                 return -EPROTO;
 122
 123         return 0;
 124 }
 125 EXPORT_SYMBOL(drm_scdc_write);
 126
 127 /**
 128  * drm_scdc_check_scrambling_status - what is status of scrambling?
 129  * @adapter: I2C adapter for DDC channel
 130  *
 131  * Reads the scrambler status over SCDC, and checks the
 132  * scrambling status.
 133  *
 134  * Returns:
 135  * True if the scrambling is enabled, false otherwise.
 136  */
 137 bool drm_scdc_get_scrambling_status(struct i2c_adapter *adapter)
 138 {
 139         u8 status;
 140         int ret;
 141
 142         ret = drm_scdc_readb(adapter, SCDC_SCRAMBLER_STATUS, &status);
 143         if (ret < 0) {
 144                 DRM_ERROR("Failed to read scrambling status: %d\n", ret);
 145                 return false;
 146         }
 147
 148         return status & SCDC_SCRAMBLING_STATUS;
 149 }
 150 EXPORT_SYMBOL(drm_scdc_get_scrambling_status);
 151
 152 /**
 153  * drm_scdc_set_scrambling - enable scrambling
 154  * @adapter: I2C adapter for DDC channel
 155  * @enable: bool to indicate if scrambling is to be enabled/disabled
 156  *
 157  * Writes the TMDS config register over SCDC channel, and:
 158  * enables scrambling when enable = 1
 159  * disables scrambling when enable = 0
 160  *
 161  * Returns:
 162  * True if scrambling is set/reset successfully, false otherwise.
 163  */
 164 bool drm_scdc_set_scrambling(struct i2c_adapter *adapter, bool enable)
 165 {
 166         u8 config;
 167         int ret;
 168
 169         ret = drm_scdc_readb(adapter, SCDC_TMDS_CONFIG, &config);
 170         if (ret < 0) {
 171                 DRM_ERROR("Failed to read TMDS config: %d\n", ret);
 172                 return false;
 173         }
 174
 175         if (enable)
 176                 config |= SCDC_SCRAMBLING_ENABLE;
 177         else
 178                 config &= ~SCDC_SCRAMBLING_ENABLE;
 179
 180         ret = drm_scdc_writeb(adapter, SCDC_TMDS_CONFIG, config);
 181         if (ret < 0) {
 182                 DRM_ERROR("Failed to enable scrambling: %d\n", ret);
 183                 return false;
 184         }
 185
 186         return true;
 187 }
 188 EXPORT_SYMBOL(drm_scdc_set_scrambling);
 189
 190 /**
 191  * drm_scdc_set_high_tmds_clock_ratio - set TMDS clock ratio
 192  * @adapter: I2C adapter for DDC channel
 193  * @set: ret or reset the high clock ratio
 194  *
 195  *
 196  *      TMDS clock ratio calculations go like this:
 197  *              TMDS character = 10 bit TMDS encoded value
 198  *
 199  *              TMDS character rate = The rate at which TMDS characters are
 200  *              transmitted (Mcsc)
 201  *
 202  *              TMDS bit rate = 10x TMDS character rate
 203  *
 204  *      As per the spec:
 205  *              TMDS clock rate for pixel clock < 340 MHz = 1x the character
 206  *              rate = 1/10 pixel clock rate
 207  *
 208  *              TMDS clock rate for pixel clock > 340 MHz = 0.25x the character
 209  *              rate = 1/40 pixel clock rate
 210  *
 211  *      Writes to the TMDS config register over SCDC channel, and:
 212  *              sets TMDS clock ratio to 1/40 when set = 1
 213  *
 214  *              sets TMDS clock ratio to 1/10 when set = 0
 215  *
 216  * Returns:
 217  * True if write is successful, false otherwise.
 218  */
 219 bool drm_scdc_set_high_tmds_clock_ratio(struct i2c_adapter *adapter, bool set)
 220 {
 221         u8 config;
 222         int ret;
 223
 224         ret = drm_scdc_readb(adapter, SCDC_TMDS_CONFIG, &config);
 225         if (ret < 0) {
 226                 DRM_ERROR("Failed to read TMDS config: %d\n", ret);
 227                 return false;
 228         }
 229
 230         if (set)
 231                 config |= SCDC_TMDS_BIT_CLOCK_RATIO_BY_40;
 232         else
 233                 config &= ~SCDC_TMDS_BIT_CLOCK_RATIO_BY_40;
 234
 235         ret = drm_scdc_writeb(adapter, SCDC_TMDS_CONFIG, config);
 236         if (ret < 0) {
 237                 DRM_ERROR("Failed to set TMDS clock ratio: %d\n", ret);
 238                 return false;
 239         }
 240
 241         /*
 242          * The spec says that a source should wait minimum 1ms and maximum
 243          * 100ms after writing the TMDS config for clock ratio. Lets allow a
 244          * wait of upto 2ms here.
 245          */
 246         usleep_range(1000, 2000);
 247         return true;
 248 }
 249 EXPORT_SYMBOL(drm_scdc_set_high_tmds_clock_ratio);