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Update some comments; no functional changes. Some historical old comments

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in this driver indicate that the SD_CAPA register is write-once and after
being set one time the values in it cannot be changed.  That turns out not
to be the case -- the values written to it survive a reset, but they can
be rewritten/changed at any time.
This commit is contained in:
Ian Lepore 2019-10-16 16:26:35 +00:00
parent d436d6e96f
commit caf894f793
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=353653
1 changed files with 5 additions and 6 deletions
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11
sys/arm/ti/ti_sdhci.c
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@ -481,10 +481,10 @@ ti_sdhci_hw_init(device_t dev)
/*
* The attach() routine has examined fdt data and set flags in
* slot.host.caps to reflect what voltages we can handle. Set those
* values in the CAPA register. The manual says that these values can
* only be set once, "before initialization" whatever that means, and
* that they survive a reset. So maybe doing this will be a no-op if
* u-boot has already initialized the hardware.
* values in the CAPA register. Empirical testing shows that the
* values in this register can be overwritten at any time, but the
* manual says that these values should only be set once, "before
* initialization" whatever that means, and that they survive a reset.
*/
regval = ti_mmchs_read_4(sc, MMCHS_SD_CAPA);
if (sc->slot.host.caps & MMC_OCR_LOW_VOLTAGE)
@ -528,8 +528,7 @@ ti_sdhci_attach(device_t dev)
* device, and only 1p8v on other devices unless an external transceiver
* is used. The only way we could know about a transceiver is fdt data.
* Note that we have to do this before calling ti_sdhci_hw_init() so
* that it can set the right values in the CAPA register, which can only
* be done once and never reset.
* that it can set the right values in the CAPA register.
*/
sc->slot.host.caps |= MMC_OCR_LOW_VOLTAGE;
if (sc->mmchs_clk_id == MMC1_CLK || OF_hasprop(node, "ti,dual-volt")) {