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Diffstat (limited to 'kernel/Documentation/bus-devices')
| -rw-r--r-- | kernel/Documentation/bus-devices/ti-gpmc.txt | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/kernel/Documentation/bus-devices/ti-gpmc.txt b/kernel/Documentation/bus-devices/ti-gpmc.txt new file mode 100644 index 000000000..cc9ce57e0 --- /dev/null +++ b/kernel/Documentation/bus-devices/ti-gpmc.txt @@ -0,0 +1,122 @@ +GPMC (General Purpose Memory Controller): +========================================= + +GPMC is an unified memory controller dedicated to interfacing external +memory devices like + * Asynchronous SRAM like memories and application specific integrated + circuit devices. + * Asynchronous, synchronous, and page mode burst NOR flash devices + NAND flash + * Pseudo-SRAM devices + +GPMC is found on Texas Instruments SoC's (OMAP based) +IP details: http://www.ti.com/lit/pdf/spruh73 section 7.1 + + +GPMC generic timing calculation: +================================ + +GPMC has certain timings that has to be programmed for proper +functioning of the peripheral, while peripheral has another set of +timings. To have peripheral work with gpmc, peripheral timings has to +be translated to the form gpmc can understand. The way it has to be +translated depends on the connected peripheral. Also there is a +dependency for certain gpmc timings on gpmc clock frequency. Hence a +generic timing routine was developed to achieve above requirements. + +Generic routine provides a generic method to calculate gpmc timings +from gpmc peripheral timings. struct gpmc_device_timings fields has to +be updated with timings from the datasheet of the peripheral that is +connected to gpmc. A few of the peripheral timings can be fed either +in time or in cycles, provision to handle this scenario has been +provided (refer struct gpmc_device_timings definition). It may so +happen that timing as specified by peripheral datasheet is not present +in timing structure, in this scenario, try to correlate peripheral +timing to the one available. If that doesn't work, try to add a new +field as required by peripheral, educate generic timing routine to +handle it, make sure that it does not break any of the existing. +Then there may be cases where peripheral datasheet doesn't mention +certain fields of struct gpmc_device_timings, zero those entries. + +Generic timing routine has been verified to work properly on +multiple onenand's and tusb6010 peripherals. + +A word of caution: generic timing routine has been developed based +on understanding of gpmc timings, peripheral timings, available +custom timing routines, a kind of reverse engineering without +most of the datasheets & hardware (to be exact none of those supported +in mainline having custom timing routine) and by simulation. + +gpmc timing dependency on peripheral timings: +[<gpmc_timing>: <peripheral timing1>, <peripheral timing2> ...] + +1. common +cs_on: t_ceasu +adv_on: t_avdasu, t_ceavd + +2. sync common +sync_clk: clk +page_burst_access: t_bacc +clk_activation: t_ces, t_avds + +3. read async muxed +adv_rd_off: t_avdp_r +oe_on: t_oeasu, t_aavdh +access: t_iaa, t_oe, t_ce, t_aa +rd_cycle: t_rd_cycle, t_cez_r, t_oez + +4. read async non-muxed +adv_rd_off: t_avdp_r +oe_on: t_oeasu +access: t_iaa, t_oe, t_ce, t_aa +rd_cycle: t_rd_cycle, t_cez_r, t_oez + +5. read sync muxed +adv_rd_off: t_avdp_r, t_avdh +oe_on: t_oeasu, t_ach, cyc_aavdh_oe +access: t_iaa, cyc_iaa, cyc_oe +rd_cycle: t_cez_r, t_oez, t_ce_rdyz + +6. read sync non-muxed +adv_rd_off: t_avdp_r +oe_on: t_oeasu +access: t_iaa, cyc_iaa, cyc_oe +rd_cycle: t_cez_r, t_oez, t_ce_rdyz + +7. write async muxed +adv_wr_off: t_avdp_w +we_on, wr_data_mux_bus: t_weasu, t_aavdh, cyc_aavhd_we +we_off: t_wpl +cs_wr_off: t_wph +wr_cycle: t_cez_w, t_wr_cycle + +8. write async non-muxed +adv_wr_off: t_avdp_w +we_on, wr_data_mux_bus: t_weasu +we_off: t_wpl +cs_wr_off: t_wph +wr_cycle: t_cez_w, t_wr_cycle + +9. write sync muxed +adv_wr_off: t_avdp_w, t_avdh +we_on, wr_data_mux_bus: t_weasu, t_rdyo, t_aavdh, cyc_aavhd_we +we_off: t_wpl, cyc_wpl +cs_wr_off: t_wph +wr_cycle: t_cez_w, t_ce_rdyz + +10. write sync non-muxed +adv_wr_off: t_avdp_w +we_on, wr_data_mux_bus: t_weasu, t_rdyo +we_off: t_wpl, cyc_wpl +cs_wr_off: t_wph +wr_cycle: t_cez_w, t_ce_rdyz + + +Note: Many of gpmc timings are dependent on other gpmc timings (a few +gpmc timings purely dependent on other gpmc timings, a reason that +some of the gpmc timings are missing above), and it will result in +indirect dependency of peripheral timings to gpmc timings other than +mentioned above, refer timing routine for more details. To know what +these peripheral timings correspond to, please see explanations in +struct gpmc_device_timings definition. And for gpmc timings refer +IP details (link above). |