Re: [Scst-devel] Issue in scst_user and rdy_to_xfer() SGL

[Vladislav B. <vs...@vl...>]

Hi Praveen,

Praveen Gokina wrote on 09/27/2016 10:05 PM:
> Hi Vlad,
> 
> We are handling reutrn value of pci_map_sg()
> 
> io->tgt_io.seg_cnt =  pci_map_sg(io->ocs->ocs_os.pdev, io->tgt_io.sg, io->tgt_io.sg_cnt,
> scst_to_tgt_dma_dir(scst_cmd_get_data_direction(cmd)));
> 
> Please let me know if we need to initialize anything in driver before calling
> pci_map_sg() ?

You need to initialize pdev you are sending to pci_map_sg(). How to do this is quite a
big and HW specific topic. I'm afraid, I can't help much here. I would suggest you to
grep pci_map_sg and dma_map_sg in Documentation subdirectory of your kernel sources tree.

Vlad

> Thanks,
> Praveen.
> 
> On Wed, Sep 28, 2016 at 10:27 AM, Vladislav Bolkhovitin <vs...@vl...
> <mailto:vs...@vl...>> wrote:
> 
> 
>     Praveen Gokina wrote on 09/27/2016 09:48 PM:
>     > Hi Vlad,
>     >
>     > We are calling pci_map_sg
>     >
>     >
>     >         io->tgt_io.sg <http://tgt_io.sg> <http://tgt_io.sg> = scst_cmd_get_sg(cmd);
>     >         io->tgt_io.sg_cnt = scst_cmd_get_sg_cnt(cmd);
>     >         io->tgt_io.bufflen = scst_cmd_get_bufflen(cmd);
>     >         io->tgt_io.is_read = scst_cmd_get_data_direction(cmd) != SCST_DATA_WRITE
>     ? 1 : 0;
>     >
>     > pci_map_sg(io->ocs->ocs_os.pdev, io->tgt_io.sg <http://tgt_io.sg>, io->tgt_io.sg_cnt,
>     > scst_to_tgt_dma_dir(scst_cmd_get_data_direction(cmd)));
> 
>     Then after pci_map_sg() sg_dma_len() should return correct value, or it would be a bug
>     in the kernel DMA subsystem, or, probably, you might not initialize it fully correctly.
>     SCST does not anyhow touch those DMA SG values.
> 
>     BTW, you can not ignore pci_map_sg() return value, it returns number of mapped SG
>     entries.
> 
>     Vlad
> 
>     > Thanks,
>     > Praveen.
>     >
>     >
>     > On Wed, Sep 28, 2016 at 10:14 AM, Vladislav Bolkhovitin <vs...@vl...
>     <mailto:vs...@vl...>
>     > <mailto:vs...@vl... <mailto:vs...@vl...>>> wrote:
>     >
>     >     Hi Praveen,
>     >
>     >     In order sg_dma_len() return correct result you need at firs map your sg by
>     >     pci_map_sg()/dma_map_sg(). Have you done this?
>     >
>     >     Vlad
>     >
>     >     Praveen Gokina wrote on 09/27/2016 08:35 PM:
>     >     > In rdy_to_xfer() driver function,
>     >     >
>     >     > we are getting bufflen as 0x200 ( 512 bytes ) as returned by
>     >     scst_cmd_get_bufflen(cmd);
>     >     >
>     >     > From the SGL,
>     >     >    sg = scst_cmd_get_sg(cmd);
>     >     >    sg_dma_len(sg) is coming as 0x400 ( 1024 bytes ).
>     >     >
>     >     > bufflen is coming correctly as 512 bytes. Whereas sg_dma_len(sg) is coming
>     as 0x400 (
>     >     > 1024 bytes ).
>     >     >
>     >     > Does driver need to call any other function to get correct sg->length ?