Author: ian
Date: Wed Oct 16 16:26:35 2019
New Revision: 353653
URL: https://svnweb.freebsd.org/changeset/base/353653
Log:
Update some comments; no functional changes. Some historical old comments
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.
Modified:
head/sys/arm/ti/ti_sdhci.c
Modified: head/sys/arm/ti/ti_sdhci.c
==============================================================================
--- head/sys/arm/ti/ti_sdhci.c Wed Oct 16 16:19:21 2019 (r353652)
+++ head/sys/arm/ti/ti_sdhci.c Wed Oct 16 16:26:35 2019 (r353653)
@@ -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")) {
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