Hi Roger, On Tue, Feb 17, 2015 at 9:12 AM, Roger Quadros <rogerq@xxxxxx> wrote: > > Can you use the following wording from TRM instead? > > as per am335x TRM (spruh73i.pdf), section 7.1.3.3.8.3.2 > > The WAITMONITORINGTIME is expressed as a number of GPMC_CLK clock cycles, > even though the access is defined as asynchronous, and no GPMC_CLK clock > is provided to the external device. Still, GPMCFCLKDIVIDER is used as a divider > for the GPMC clock, so it must be programmed to define the > correct WAITMONITORINGTIME delay. Verbatim? Sure can. Gonna do that with a rebase to 3.19, I guess. > > Instead of this can we explicitly set the GPMC_CLK divider to 1 and hence > corresponding divider bits to 0 in the asynchronous case? > This is because the previously calculated "div" depends on synchronous clock which > might not be properly initialized for asynchronous devices. No, we shouldn't. If WAITREADMONITORING and/or WAITWRITEMONITORING is enabled, sync_clk must be set in order to use WAITMONITORINGTIME correctly. If it's not explicitly set, it's set to 0, which yields div 1 anyways. The reason being that a fixed divider of 1 will limit a user's ability to prolong the #WAIT-deassert --> *access delay for no good reason. If working with a slow device, this will inconvenience users. > > AFAIK t->sync_clk is always 0 for asynchronous devices and gpmc_calc_divider(0) > will return 1 and your patch will work but still we shouldn't depend on sync_clk for > asynchronous devices so let's set this explicitly. See above. Hardware depends on divider, divider is set by sync_clk, so we shouldn't limit what a user can program in DT. Having said that, I'm not aware that sync_clk is always 0 for async devices. The code always parses it and sets the appropriate field in gpmc_t, which is passed to gpmc_cs_set_timings. Now, there is generally a lack of checking for optional/required DT properties, so I didn't add extra checking. Regards, Robert -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
