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SubjectRicoh R5C822 and QUIRK_FORCE_DMA
Hi,

I recently got a used Thinkpad X41, which has a built-in Ricoh
R5C822 Rev 13 SD controller, which seems to only use dma if I add
the FORCE_DMA quirk:

|04:00.1 SD Host controller: Ricoh Co Ltd R5C822 SD/SDIO/MMC/MS/MSPro
|Host Adapter (rev 13)
| Subsystem: IBM ThinkPad X60s / Z60t
| Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop-
|ParErr- Stepping- SERR+ FastB2B- DisINTx-
| Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
| Latency: 64
| Interrupt: pin B routed to IRQ 17
| Region 0: Memory at a0201000 (32-bit, non-prefetchable) [size=256]
| Capabilities: [80] Power Management version 2
| Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=0mA PME(D0+,D1+,D2+,D3hot+,D3cold+)
| Status: D0 PME-Enable- DSel=0 DScale=2 PME-
| Kernel driver in use: sdhci-pci
|00: 80 11 22 08 06 01 10 02 13 00 05 08 00 40 80 00
|10: 00 10 20 a0 00 00 00 00 00 00 00 00 00 00 00 00
|20: 00 00 00 00 00 00 00 00 00 00 00 00 14 10 56 05
|30: 00 00 00 00 80 00 00 00 00 00 00 00 0b 02 00 00
|40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|80: 01 00 02 fe 00 40 00 48 00 00 00 00 00 00 00 00
|90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|a0: 00 00 00 00 00 00 00 00 00 00 00 00 14 10 56 05
|b0: 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00
|c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|e0: a1 21 80 01 00 00 00 00 40 00 00 00 00 00 00 00
|f0: 00 00 00 00 00 00 00 00 03 00 20 04 00 00 00 00

I found that (using 2.6.30-rc4) the SD controller is rather slow and
makes the X cursor jumpy, so I suspected it is using PIO rather than
DMA. vmstat also showed a high system percentage instead of just
iowait.

After adding a 'No DMA available' debugging statement I found that
this revision does not seem to claim DMA support. However, after
seeing in some dmesg logs that at least Rev 18 and greater do
support DMA, I thought I'd try to add SDHCI_QUIRK_FORCE_DMA to
sdhci-pci.c.

Lo and behold, the speed has now doubled (4MB/s vs. nearly 8MB/s),
the mouse cursor is no longer jumpy and system percentage is down to
5% with 95% iowait.

Do you know any controller bugs for this revision which may be the
reason for not advertising DMA capability?
I haven't done any big tests yet, but at first glance it seems to
read/write the card just fine.

HTH,

--
Tobias PGP: http://9ac7e0bc.uguu.de


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