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drm/i915/skl: Deinit/init the display at suspend/resume
We need to re-init the display hardware when going out of suspend. This
includes:
- Hooking the PCH to the reset logic
- Restoring CDCDLK
- Enabling the DDB power
Among those, only the CDCDLK one is a bit tricky. There's some
complexity in that:
- DPLL0 (which is the source for CDCLK) has two VCOs, each with a set
of supported frequencies. As eDP also uses DPLL0 for its link rate,
once DPLL0 is on, we restrict the possible eDP link rates the chosen
VCO.
- CDCLK also limits the bandwidth available to push pixels.
So, as a first step, this commit restore what the BIOS set, until I can
do more testing.
In case that's of interest for the reviewer, I've unit tested the
function that derives the decimal frequency field:
#include <stdio.h>
#include <stdint.h>
#include <assert.h>
#define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
static const struct dpll_freq {
unsigned int freq;
unsigned int decimal;
} freqs[] = {
{ .freq = 308570, .decimal = 0b01001100111},
{ .freq = 337500, .decimal = 0b01010100001},
{ .freq = 432000, .decimal = 0b01101011110},
{ .freq = 450000, .decimal = 0b01110000010},
{ .freq = 540000, .decimal = 0b10000110110},
{ .freq = 617140, .decimal = 0b10011010000},
{ .freq = 675000, .decimal = 0b10101000100},
};
static void intbits(unsigned int v)
{
int i;
for(i = 10; i >= 0; i--)
putchar('0' + ((v >> i) & 1));
}
static unsigned int freq_decimal(unsigned int freq /* in kHz */)
{
return (freq - 1000) / 500;
}
static void test_freq(const struct dpll_freq *entry)
{
unsigned int decimal = freq_decimal(entry->freq);
printf("freq: %d, expected: ", entry->freq);
intbits(entry->decimal);
printf(", got: ");
intbits(decimal);
putchar('\n');
assert(decimal == entry->decimal);
}
int main(int argc, char **argv)
{
int i;
for (i = 0; i < ARRAY_SIZE(freqs); i++)
test_freq(&freqs[i]);
return 0;
}
v2:
- Rebase on top of -nightly
- Use (freq - 1000) / 500 for the decimal frequency (Ville)
- Fix setting the enable bit of HSW_NDE_RSTWRN_OPT (Ville)
- Rename skl_display_{resume,suspend} to skl_{init,uninit}_cdclk to
be consistent with the BXT code (Ville)
- Store boot CDCLK in ddi_pll_init (Ville)
- Merge dev_priv's skl_boot_cdclk into cdclk_freq
- Use LCPLL_PLL_LOCK instead of (1 << 30) (Ville)
- Replace various '0' by SKL_DPLL0 to be a bit more explicit that
we're programming DPLL0
- Busy poll the PCU before doing the frequency change. It takes about
3/4 cycles, each separated by 10us, to get the ACK from the CPU
(Ville)
v3:
- Restore dev_priv->skl_boot_cdclk, leaving unification with
dev_priv->cdclk_freq for a later patch (Daniel, Ville)
Reviewed-by: 
Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>