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diff --git a/Documentation/driver-api/memory-devices/ti-gpmc.rst b/Documentation/driver-api/memory-devices/ti-gpmc.rst new file mode 100644 index 000000000..b1bb86871 --- /dev/null +++ b/Documentation/driver-api/memory-devices/ti-gpmc.rst @@ -0,0 +1,179 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================== +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: https://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). |