On 07/06/2016 01:46 AM, Jon Hunter wrote:
On 06/07/16 03:14, Alexandre Courbot wrote:
On Tue, Jul 5, 2016 at 11:07 PM, Jon Hunter <jonathanh@xxxxxxxxxx> wrote:
To support UHS modes for Tegra an external regulator must be present
to adjust the IO voltage accordingly. If the regulator is not present
but the host supports the UHS modes and the SD/MMC device supports the
UHS modes, then we will attempt to switch to a high-speed mode.
Without an external regulator, Tegra will fail to switch to the
high-speed mode. Although this is expected, it has been found that with
some SD cards, once it has been switched to operate at a high-speed
mode and hence a lower IO voltage, if the IO voltage is not changed then
all subsequent commands issues to the card will fail. Furthermore, it
will not be possible to switch back to a non high-speed mode and so
eventually the SD card initialisation will fail.
The SDHCI core does not require that the host have an external regulator
when switching to UHS modes and therefore, the Tegra SDHCI host
controller should only advertise the UHS modes as being supported if the
regulator for the IO voltage is present. Fortunately, Tegra has a vendor
specific register which can be used to control which modes are
advertised via the SDHCI_CAPABILITIES register and if the controller is
compatible with v3.0 of the SDHCI specification. Hence, if there is no
IO voltage regulator present in device-tree for the Tegra SDHCI host, then
don't advertise the UHS modes or that the controller is SDHCI v3.0
compatible.
Note that if the SDHCI is compatible with v3.0 of the SDHCI specification
then this will cause the SDHCI core to read the SDHCI_CAPABILITIES_1
register which will enable other UHS modes.
This fixes commit 7ad2ed1dfcbe ("mmc: tegra: enable UHS-I modes") which
enables UHS mode without checking if the board can support them.
Fixes: 7ad2ed1dfcbe ("mmc: tegra: enable UHS-I modes")
Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
---
Please note that I have been reviewing the series from Adrian [0] to
make it easier for drivers to set the capabilities. However, given that
we can control the capabilities that are advertised by the CAPS registers
it seems easier to use this feature.
[0] http://marc.info/?l=linux-mmc&m=146712062816835&w=2
diff --git a/drivers/mmc/host/sdhci-tegra.c b/drivers/mmc/host/sdhci-tegra.c
+
+ /*
+ * If the board does not define a regulator for the SDHCI
+ * IO voltage, then don't advertise support for UHS modes
+ * even if the device supports it because the IO voltage
+ * cannot be configured.
+ */
+ if (of_property_read_bool(dev->of_node, "vqmmc-supply")) {
Can't you check whether (!IS_SERR(host->mmc->supply.vqmmc)) instead?
The property being present doesn't necessarily guarantee that the
regulator has been obtained successfully.
The problem is that the regulator is obtained after the reset occurs and
so unfortunately that won't work either :-(
I wonder if we should request the regulator during the Tegra SDHCI probe
before we call sdhci_add_host(). This would allow us to defer the probe
if it is missing/not present.
Yes, any resource acquisition must happen in probe(). There's no way
around that.
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