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The mmc workqueue is an ordered workqueue, allowing only one work to execute per given time. As this workqueue is used for card detection, the conseqeunce is that cards will be detected one by one waiting for each other. Moreover, most of the time spent during card initialization is waiting for the card's internal firmware to be ready. From a CPU perspective this typically means waiting for a completion variable to be kicked via an IRQ-handler or waiting for a sleep timer to finish. This behaviour of detecting/initializing cards is sub-optimal, especially for SOCs having several controllers/cards. Let's convert to use the system_freezable_wq for the mmc detect works. This enables several works to be executed simultaneously and thus also cards to be detected like so. Tests on UX500, which holds two eMMC cards and an SD-card (actually also an SDIO card, currently not detected), shows a significant improved behaviour due to this change. Before this change, both the eMMC cards waited for the SD card to be initialized as its detect work entered the workqueue first. In some cases, depending on the characteristic of the SD-card, they got delayed 1-1.5 s. Additionally for the second eMMC, it needed to wait for the first eMMC to be initialized which added another 120-190 ms. Converting to the system_freezable_wq, removed these delays and made both the eMMC cards available far earlier in the boot sequence. Selecting the system_freezable_wq, in favour of for example the system_wq, is because we need card detection mechanism to be disabled once userspace are frozen during system PM. Currently the mmc core deal with this via PM notifiers, but following patches may utilize the behaviour of the system_freezable_wq, to simplify the use of the PM notifiers. Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> Tested-by: Alan Cooper <alcooperx@gmail.com> Tested-by: Shawn Lin <shawn.lin@rock-chips.com> |
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