Mount root from SD card?

[Krassimir Slavchev]

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M. Warner Losh wrote:
> In message: <497896F3.9030908 at bulinfo.net>
>             Krassimir Slavchev <krassi at bulinfo.net> writes:
> : Index: at91_mci.c
> : ===================================================================
> : --- at91_mci.c	(revision 187590)
> : +++ at91_mci.c	(working copy)
> : @@ -199,7 +199,7 @@
> :  		goto out;
> :  	}
> :  	sc->host.f_min = 375000;
> : -	sc->host.f_max = at91_master_clock / 2;	/* Typically 30MHz */
> : +	sc->host.f_max = AT91C_MASTER_CLOCK / 2;	/* Typically 30MHz */
> :  	sc->host.host_ocr = MMC_OCR_320_330 | MMC_OCR_330_340;
> :  	if (sc->wire4)
> :  		sc->host.caps = MMC_CAP_4_BIT_DATA;
> 
> This change is wrong.

Ok. I did this because at91_master_clock was not defined here.

> 
> : @@ -399,8 +399,8 @@
> :  	WR4(sc, MCI_ARGR, cmd->arg);
> :  	if (cmdr & MCI_CMDR_TRCMD_START) {
> :  		if (cmdr & MCI_CMDR_TRDIR) {
> : +			WR4(sc, MCI_CMDR, cmdr);
> :  			WR4(sc, PDC_PTCR, PDC_PTCR_RXTEN);
> : -			WR4(sc, MCI_CMDR, cmdr);
> 
> This change is also wrong.  It won't work.  Also, why test the
> direction at all if we're just going to do the same thing in both legs
> of the branch?  When I was developing the code, I originally had the
> 'send a command and then enable PDC' logic.  It didn't work for the
> read case, so now we enable the reader and then send the command.  We
> do this based on the logic that it is OK to have the PDC enabled when
> there's no data transfer going, but if we send the command, then take
> an interrupt before we can enable the PDC, we'd lose data.  And that
> seemed to happen a lot.

Ok but I was able to read correctly first blocks ...
Looking at linux's driver they do the same, first sending CMD and then
enable PDC for reading.

Thanks for latest fixes!

Best regards

> 
> There's lots of races in programming this chip :(
> 
> :  		} else {
> :  			WR4(sc, MCI_CMDR, cmdr);
> :  			WR4(sc, PDC_PTCR, PDC_PTCR_TXTEN);
> 
> 
> Warner
> 


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