Messages in this thread | | | From | Wolfgang Mües <> | Subject | Re: [PATCH] mmc_spi: fail gracefully if host or card do not support the switch command | Date | Mon, 15 Jun 2009 10:36:05 +0200 |
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Hello Pierre,
Am Samstag, 13. Juni 2009 schrieb Pierre Ossman: > > The switch command (typically speed switching from 25 to 50 MHz clock) > > can be rejected by _both_ the host controller/driver and by the card. > > Elder revisions of the SD card do not support speed switching. > > Fail gracefully if the reject is comming from the card.
> Have you ever seen this in practice?
Yes, I have. An old 1 GByte SD card.
> For SD there are several checks > before the switch command is actually issued.
But there are two cases not covered by these checks:
a) the switch command is supported, but the card is not capable of switching to 50 MHz.
b) the card rejects the switch command in SPI mode, because it is not mandatory here.
So yes, the checks can be improved. But only extending the error codes was a simple, fast and minimal solution.
regards
i. A. Wolfgang Mües -- Auerswald GmbH & Co. KG Hardware Development Telefon: +49 (0)5306 9219 0 Telefax: +49 (0)5306 9219 94 E-Mail: Wolfgang.Mues@Auerswald.de Web: http://www.auerswald.de -------------------------------------------------------------- Auerswald GmbH & Co. KG, Vor den Grashöfen 1, 38162 Cremlingen Registriert beim AG Braunschweig HRA 13289 p.h.G Auerswald Geschäftsführungsges. mbH Registriert beim AG Braunschweig HRB 7463 Geschäftsführer: Dipl-Ing. Gerhard Auerswald -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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