fixing mpii(4) for tls_maxphys

[Emmanuel Dreyfus <Emmanuel.Dreyfus%espci.fr@localhost>]

Hi

I am still trying - without much success - to fix mpii(4) for tls_maxphys.

The board is known to support 512 kB blocks. I tried building a tls_maxphys
kernel with MAXPHYS set to 1024 kB, but this is not enough to get it
working. I identified two problems.

First problem: the worst case scenario for a 512 kB transfer is 128
different pages, which a bus_dmamap_t with 128 segments. I understand
mpii(4) need additional "chaining" segements, and debug printfs
have shown it uses at most 141 segments in my test case, otherwise
I get a EFBIG. Ths bus_dmamap_t segment count is set here: 

               if (bus_dmamap_create(sc->sc_dmat, MAXPHYS,
                   sc->sc_max_sgl_len, MAXPHYS, 0,
                   BUS_DMA_NOWAIT | BUS_DMA_ALLOCNOW,
                   &ccb->ccb_dmamap) != 0) {

With sc->sc_max_sgl_len set from MPII_MAX_SGL (currently 32)
minus chaining entries count. Let's say we need to set MPII_MAX_SGL to
256 segments until I understand the whole thing. The MAXPHYS here also
needs to be changed into MPII_MAXFER:

#define MPII_MAX_SGL    256
(...)
#define MPII_MAXFER     (512 * 1024)
(...)
               if (bus_dmamap_create(sc->sc_dmat, MPII_MAXFER,
                   sc->sc_max_sgl_len, MPII_MAXFER, 0,
                   BUS_DMA_NOWAIT | BUS_DMA_ALLOCNOW,
                   &ccb->ccb_dmamap) != 0) {

Second problem: MPII_MAX_SGL is used to set the size of mcb->mcb_sgl:

struct mpii_ccb_bundle {
        struct mpii_msg_scsi_io mcb_io; /* sgl must follow */
        struct mpii_sge         mcb_sgl[MPII_MAX_SGL];
        struct scsi_sense_data  mcb_sense;
} __packed;

If I set it higher than 32, the adapter complains about invalid SGL,
and I do not get sense data reported anymore (it is all zeroes). This
suggests struct mpii_ccb_bundle size is mandated by the adapter. But 
if that is the case, how can I manage to perform a 512 kB transfer with 
4 kB pages?

Obviously I am missing something.


-- 
Emmanuel Dreyfus
ESPCI ParisTech - Service informatique
Emmanuel.Dreyfus%espci.fr@localhost