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��.n��������+%������w��{.n�����{��i��)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
