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From: Ulf Hansson <firstname.lastname@example.org>
To: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Cc: "email@example.com" <firstname.lastname@example.org>,
Subject: Re: [RFC 0/2] dw_mmc: add multislot support
Date: Fri, 20 Apr 2018 10:56:46 +0200 [thread overview]
Message-ID: <CAPDyKFqGNR_YV=adUKqzEuYk-ZV48MHW68Uyr=8nXBEvafGsWQ@mail.gmail.com> (raw)
On 20 April 2018 at 09:42, Alexey Brodkin <Alexey.Brodkin@synopsys.com> 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)?
> 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
next prev parent reply other threads:[~2018-04-20 8:56 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20180417121325epcas2p319c672feee4203d8b90131da461f4bd6@epcas2p3.samsung.com>
2018-04-17 12:11 ` Eugeniy Paltsev
2018-04-17 12:11 ` [RFC 1/2] dw_mmc: revert removal " Eugeniy Paltsev
2018-04-17 12:11 ` [RFC 2/2] dw_mmc: add " Eugeniy Paltsev
2018-04-20 7:35 ` [RFC 0/2] " Ulf Hansson
2018-04-20 7:42 ` Alexey Brodkin
2018-04-20 8:56 ` Ulf Hansson [this message]
2018-04-20 15:53 ` Eugeniy Paltsev
2018-04-23 6:47 ` Ulf Hansson
2018-04-25 13:53 ` Eugeniy Paltsev
2018-04-26 6:28 ` Ulf Hansson
2018-04-26 10:30 ` Jaehoon Chung
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