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+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).