On 17/02/15 15:34, Robert Abel wrote: > Hi Roger, > > On Tue, Feb 17, 2015 at 9:12 AM, Roger Quadros <rogerq@xxxxxx <mailto: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. nobody stops the DT binding from specifying a large enough "gpmc,wait-monitoring-ns" value. The driver must use that to scale the GPMC_CLK if it doesn't fit in the GPMC_FCLK. This feature can come separately though. So for now I was suggesting to set the divisor to 1. What I'm stressing on is that there shouldn't be any dependency on "gpmc,sync-clk-ps" for asynchronous devices. It also becomes easier to specify the wait-monitoring-ns as we don't need to cross reference with "sync-clk-ps". > > > 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. AFAIK "gpmc,sync-clk-ps" is not specified for asynchronous devices so it defaults to 0 in the driver. cheers, -roger -- 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
