Hi Ulf, On Fri, 2018-04-20 at 09:35 +0200, Ulf Hansson wrote: > [...] > > > > > 2. Add missing stuff to support multislot mode in DesignWare MMC driver. > > * Add missing slot switch to __dw_mci_start_request() function. > > * Refactor set_ios function: > > a) Calculate common clock which is > > suitable for all slots instead of directly use clock value > > provided by mmc core. We calculate common clock as the minimum > > among each used slot clocks. This clock is calculated in > > dw_mci_calc_common_clock() function which is called > > from set_ios() > > b) Disable clock only if no other slots are ON. > > c) Setup clock directly in set_ios() only if no other slots > > are ON. Otherwise adjust clock in __dw_mci_start_request() > > function before slot switch. > > d) Move timings and bus_width setup to separate funcions. > > * Use timing field in each slot structure instead of common field in > > host structure. > > * Add locks to serialize access to registers. > > Sorry, but this is a hack to *try* to make multi-slot work and this > isn't sufficient. There were good reasons to why the earlier > non-working multi slot support was removed from dw_mmc. > > Let me elaborate a bit for your understanding. The core uses a host > lock (mmc_claim|release_host()) to serialize operations and commands, > as to confirm to the SD/SDIO/(e)MMC specs. The above changes gives no > guarantees for this. To make that work, we would need a "mmc bus lock" > to be managed by the core. > > However, inventing a "mmc bus lock" would lead to other problems > related to I/O scheduling for upper layers - it simply breaks. For > example, I/O requests for one card/slot can then starve I/O requests > reaching another card/slot. So are you saying that multi-slot support is a no go in general or it is only applicable to DW MMC (I really doubt that's a case)? BTW there're other controllers that seem to support multi-slot like Atmel etc. -Alexey
