Re: [PATCH 4/9] mci: add RPMB support

[Sascha Hauer <s.hauer@pengutronix.de>]

On Tue, Mar 18, 2025 at 12:33:05PM +0100, Sascha Hauer wrote:
> On Mon, Mar 17, 2025 at 04:18:32PM +0100, Ahmad Fatoum wrote:
> > Hello Sascha,
> > 
> > On 3/12/25 13:16, Sascha Hauer wrote:
> > > +
> > > +int mci_rpmb_route_frames(struct mci *mci, void *req, unsigned long reqlen,
> > > +			  void *rsp, unsigned long rsplen)
> > > +{
> > > +	/*
> > > +	 * Whoever crafted the data supplied to this function knows how to
> > > +	 * format the PRMB frames and which response is expected. If
> > > +	 * there's some unexpected mismatch it's more helpful to report an
> > > +	 * error immediately than trying to guess what was the intention
> > > +	 * and possibly just delay an eventual error which will be harder
> > > +	 * to track down.
> > > +	 */
> > > +	void *rpmb_data = NULL;
> > > +	int ret;
> > > +
> > > +	mci_blk_part_switch(mci->rpmb_part);
> > > +
> > > +	if (!IS_ALIGNED((uintptr_t)req, ARCH_DMA_MINALIGN)) {
> > 
> > Even if alignment happens to be correct, there is no guarantee that
> > there is no other data sharing a cache line.
> 
> reqlen is expected to be a single block of 512 bytes, so indeed when req
> is aligned then the end is cacheline aligned as well. We could check
> reqlen as well, but I actually never ran into this case, so we can just
> return an error for now as you suggested.

I was wrong here. the request is placed directly behind a 6 byte struct,
so it's guaranteed to be unaligned. We always have to copy it.

The response might be unaligned as well, but must be aligned to pass it
to the mmc layer. In my tests the response was always aligned, but
better safe than sorry, so I'll add an alignment check here as well,
this time including a check for the length.

Sascha

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