[linux-dvb] SAA7146 short delay flag and budget cards

Johannes Stezenbach js at linuxtv.org
Mon Sep 26 14:08:19 CEST 2005


On Mon, Sep 26, 2005 Oliver Endriss wrote:
> hunold at linuxtv.org wrote:
> > 
> > First of all, I did not add "short_delay" to that code. ;-) 
> 
> I did, see below.

Did you? Or do you confuse short_delay with SAA7146_I2C_SHORT_DELAY?
It's pretty clear why SAA7146_I2C_SHORT_DELAY exists and waht it does,
but I don't get why short_delay exists, i.e. why using udelay(10)
instead of msleep(1) isn't the default.

> Sorry, this is not correct. SAA7146_I2C_SHORT_DELAY turns on polling for
> _all_ transfers. (That's the reason why it had been added.)
> 
> |       if ( count > 3 || 0 != (SAA7146_I2C_SHORT_DELAY & dev->ext->flags) )
> |                short_delay = 1;
> 
> SAA7146_I2C_SHORT_DELAY was introduced by me because tuning with FF
> cards was rather slow. From Changelog:
> 
> | 2003-11-25 20:13  endriss
> |         * linux/: drivers/media/common/saa7146_i2c.c,
> |          drivers/media/dvb/ttpci/av7110.c, include/media/saa7146.h:
> |          introduced flag SAA7146_I2C_SHORT_DELAY to speed up I2C access
> 
> Before that, only larger transfers used polling. Since DVB cards use a
> lot of small i2c transfers there was noticeable delay during tuning.

This is incorrect, the driver always uses polling, just one time
with msleep(1) (i.e. sleep at least one scheduler tick) and the other
with udelay(1) (busy loop for 10 usecs).

> Imho the flag SAA7146_I2C_SHORT_DELAY should be added for all
> saa7146-based cards.

Unless someone can explain why short_delay==0 is necessary I vote
for removing this altogether and making the use of udelay(10)
the default.

Is short_delay==0 necessary for some analog saa7146 based cards?


Johannes



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