Re: [PATCH v3] scsi: ufs: Increase the maximum data buffer size

[Bean Huo <huobean@gmail.com>]

On Wed, 2022-08-03 at 09:23 -0700, Bart Van Assche wrote:
> On 8/2/22 16:40, yohan.joung@sk.com wrote:
> > Is it possible by adding only max_sector to increase the data
> > buffer size?
> 
> Yes.
> 
> > I think the data buffer will split to 512 KiB, because the sg_table
> > size is SG_ALL
> 
> I don't think so. With this patch applied, the limits supported by
> the 
> UFS driver are as follows:
> 
>         .sg_tablesize           = SG_ALL,                   /* 128 */
>         .max_segment_size       = PRDT_DATA_BYTE_COUNT_MAX, /* 256
> KiB*/
>         .max_sectors            = (1 << 20) / SECTOR_SIZE,  /* 1 MiB
> */
> 
> So the maximum data buffer size is min(max_sectors * 512,
> sg_tablesize * 
> max_segment_size) = min(1 MiB, 128 * 256 KiB) = 1 MiB. On a system
> with 
> 4 KiB pages, the data buffer size will be 128 * 4 KiB = 512 MiB if
> none 
> of the pages involved in the I/O are contiguous.
> 
> Bart.


Bart, 

This change just increases the shost->max_sectors limit from 501KB to
1Mb, but the final value will be overridden by the optimal transfer
length defined in the VPD, right?

Kind regards,
Bean