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https://github.com/brain-hackers/u-boot-brain
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f8e88b6837
Before driving the CKE pin (Clock Enable) high, the DDR3 spec requires to wait for additional 500 us after the RESET pin is de-asserted. The DRAM controller takes care of this delay by itself, using a configurable counter in the SDR_IDCR register. This works in the same way on sun4i/sun5i/sun7i hardware (even the default register value 0x00c80064 is identical). Except that the counter is ticking a bit slower on sun7i (3 DRAM clock cycles instead of 2), resulting in longer actual delays for the same settings. This patch configures the SDR_IDCR register for all sun4i/sun5i/sun7i SoC variants and not just for sun7i alone. Also an explicit udelay(500) is added immediately after DDR3 reset for extra safety. This is a duplicated functionality. But since we don't have perfect documentation, it may be reasonable to play safe. Half a millisecond boot time increase is not that significant. Boot time can be always optimized later. Preferebly by the people, who have the hardware equipment to check the actual signals on the RESET and CKE lines and verify all the timings. The old code did not configure the SDR_IDCR register for sun4i/sun5i, but performed the DDR3 reset very early for sun4i/sun5i. This resulted in a larger time gap between the DDR3 reset and the DDR3 initialization steps and reduced the chances of CKE delay timing violation to cause real troubles. Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com> Acked-by: Ian Campbell <ijc@hellion.org.uk> Signed-off-by: Hans de Goede <hdegoede@redhat.com> |
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