On Wed, Mar 18, 2015 at 10:52:24AM +0100, Tomeu Vizoso wrote:

As there isn't a way for the firmware on the Nyan chromebooks to hand over the display to the kernel.

Perhaps this should be more explicit. I'm assuming this somehow breaks on Nyan for you because we try to reprogram the SOR from an already initialized state and that doesn't actually work? Your current commit message doesn't make this sound like a fix for an actual problem.

Signed-off-by: Tomeu Vizoso tomeu.vizoso@collabora.com Acked-by: Stephen Warren swarren@nvidia.com Reviewed-by: Alexandre Courbot acourbot@nvidia.com

---

drivers/gpu/drm/tegra/sor.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/tegra/sor.c b/drivers/gpu/drm/tegra/sor.c index 2afe478..e6caacc 100644 --- a/drivers/gpu/drm/tegra/sor.c +++ b/drivers/gpu/drm/tegra/sor.c @@ -1458,6 +1458,20 @@ static int tegra_sor_probe(struct platform_device *pdev)

mutex_init(&sor->lock);

• err = reset_control_assert(sor->rst);
• if (err < 0) {

• dev_err(&pdev->dev, "failed to assert SOR reset: %d\n", err);
  

• return err;
  

• }
• msleep(20);
• err = reset_control_deassert(sor->rst);
• if (err < 0) {

• dev_err(&pdev->dev, "failed to deassert SOR reset: %d\n", err);
  

• return err;
  

• }

If you do this in ->probe() there's a potentially long time where the screen will remain black. A better location for this is probably in the tegra_sor_init() function. That puts it closer to where the output is reinitialized and potentially reduces the time where no display is available.

Also it is a more logical place for this code, since the clocks are also enabled in tegra_sor_init(). Technically resets on Tegra are synchronous and therefore the reset should happen across the clk_prepare_enable() call of the primary module clock. So I'd expect something like this:

err = reset_control_assert(sor->rst); ...

err = clk_prepare_enable(sor->clk); ...

/* sleep */

err = reset_control_deassert(sor->rst); ...

Where sleep can probably be significantly shorter than 20 ms. I think the documentation says that 2 us are typically enough. That said, I'm fine with leaving in 20 ms, it shouldn't matter much in the overall boot-time.

Also, since this will need to be revisited once we have proper hand-over from firmware to kernel, do you mind adding a comment along these lines:

/* * XXX: Remove this reset once proper hand-over from firmware to * kernel is possible. */

?

Thanks, Thierry

25.03.2015 11:59, Tomeu Vizoso пишет:

As there isn't a way for the firmware on the Nyan chromebooks to hand over the display to the kernel, and the kernel isn't redoing the whole configuration at present.

With this patch, the SOR is brought to a known state and we get correct display on every boot.

Signed-off-by: Tomeu Vizoso tomeu.vizoso@collabora.com

---

v7: * Move the reset to the host1x_client_ops.init callback as suggested by Thierry

• Reduced the time during which the reset line is asserted from

20ms to 2ms

drivers/gpu/drm/tegra/sor.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/tegra/sor.c b/drivers/gpu/drm/tegra/sor.c index 2afe478..027a25d22 100644 --- a/drivers/gpu/drm/tegra/sor.c +++ b/drivers/gpu/drm/tegra/sor.c @@ -1354,12 +1354,30 @@ static int tegra_sor_init(struct host1x_client *client) } }

• /*

• * XXX: Remove this reset once proper hand-over from firmware to
  

• * kernel is possible.
  

• */
  

• err = reset_control_assert(sor->rst);

• if (err < 0) {

• dev_err(sor->dev, "failed to assert SOR reset: %d\n", err);
  

• return err;
  

• }

• err = clk_prepare_enable(sor->clk); if (err < 0) { dev_err(sor->dev, "failed to enable clock: %d\n", err); return err; }

• msleep(2);

• err = reset_control_deassert(sor->rst);

• if (err < 0) {

• dev_err(sor->dev, "failed to deassert SOR reset: %d\n", err);
  

• return err;
  

• }

• err = clk_prepare_enable(sor->clk_safe); if (err < 0) return err;

According to kernel doc, you should use usleep_range() instead of msleep().

https://www.kernel.org/doc/Documentation/timers/timers-howto.txt