On 01/13/15 16:41, Ulf Hansson wrote:
On 13 January 2015 at 16:11, Arend van Spriel<arend@xxxxxxxxxxxx> wrote:
On 01/13/15 15:56, Ulf Hansson wrote:
[...]
Thank you for looking at the patches.
I am not sure I know what you mean. sdhci already has a re-tuning
timer, so
this is just moving it into core, where it won't be used by other
drivers
unless they enable it.
I am kind of questioning the re-tuning timer in sdhci. What is it good
for?
It is part of the SD Host Controller Standard Specification. The timer
ensures that re-tuning is done before temperature changes could affect
the
"sampling point". It is needed for re-tuning mode 1 for UHS-I modes like
SDR104.
Does the spec say what value the timer should have?
It is read from the Capabilities register in the SD host controller, ie. in
field "Timer Count for Re-Tuning" (see below).
Regards,
Arend
Timer Count for Re-Tuning
This field indicates an initial value of the Re-Tuning Timer for Re-Tuning
Mode 1 to 3. Setting to 0 disables Re-Tuning Timer.
0h Re-Tuning Timer disabled
1h 1 seconds
2h 2 seconds
3h 4 seconds
4h 8 seconds
..... ......................
n 2(n-1) seconds
..... ......................
Bh 1024 seconds
Eh - Ch Reserved
Fh Get information from other source
Thanks for sharing this information, but unfortunate I don't
understand much from it.
Is the host driver intended to read/poll this register to find a good value?
You can download the spec (and others) here [1]. sdhci currently
implements retuning mode 1, which is decribed in the spec:
Re-Tuning Timer Control Example for Re-Tuning Mode 1
The initial value of re-tuning timer is provided by Timer Count for
Re-Tuning field in this register. The timer starts counting by loading
the initial value. When the timer expires, the Host Driver marks an
expiration flag. On receiving a command request, the Host driver checks
the expiration flag. If the expiration flag is set, then the Host Driver
should perform the re-tuning procedure before issuing a command. If the
expiration flag is not set, then the Host Driver issues a command
without performing the re-tuning procedure. Every time the re-tuning
procedure is performed, the timer loads the new initial value and the
expiration flag is cleared.
So the host controller could indeed update this register for subsequent
retuning.
Regards,
Arend
[1] https://www.sdcard.org/downloads/pls/
Isn't heat one of the most important factor that could effect the need
for a re-tune? Does then the controller internally dynamically update
this register (since it keep track of heat or similar)?
Kind regards
Uffe
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