On 20 April 2018 at 09:42, Alexey Brodkin <Alexey.Brodkin@xxxxxxxxxxxx> wrote: > 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)? In general. > > BTW there're other controllers that seem to support multi-slot like Atmel etc. Yeah, none of those are working - it just bad attempts to try to make *something* work. Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
