linux-kernel - Re: [PATCHi v3] staging: rts5208: Convert kmap() to kmap_local

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Date:   Tue, 29 Mar 2022 22:34:51 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Philip <benjamin.philip495@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Colin Ian King <colin.king@...el.com>,
        Samuel Sjöberg <info@...uelsjoberg.se>,
        Charlie Sands <sandsch@...thvilleschools.net>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>,
        outreachy@...ts.linux.dev
Subject: Re: [PATCHi v3] staging: rts5208: Convert kmap() to kmap_local_page()

On Tue, Mar 29, 2022 at 06:20:55PM +0200, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page()
> where it is feasible.
> 
> With kmap_local_page(), the mapping is per thread, CPU local and not
> globally visible. Therefore rtsx_stor_access_xfer_buf() is a function
> where the use of kmap_local_page() in place of kmap() is correctly
> suited.
> 
> Convert to kmap_local_page() but, instead of open coding it, use the
> helpers memcpy_to_page() and memcpy_from_page().
> 
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
> 
> v1 -> v2: Rework the commit message and use the appropriate helpers
> instead of open coding the use of kmap_local_page()/kunmap_local_page().
> (Thanks to Ira Weiny <ira.weiny@...el.com>).
> 
> v2 -> v3: Use memcpy_{to,from}_page() arguments correctly.
> (Thanks to Dan Carpenter <dan.carpenter@...cle.com>).
> 
>  drivers/staging/rts5208/rtsx_transport.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/rts5208/rtsx_transport.c b/drivers/staging/rts5208/rtsx_transport.c
> index 805dc18fac0a..b702c7caf944 100644
> --- a/drivers/staging/rts5208/rtsx_transport.c
> +++ b/drivers/staging/rts5208/rtsx_transport.c
> @@ -92,13 +92,11 @@ unsigned int rtsx_stor_access_xfer_buf(unsigned char *buffer,
>  			while (sglen > 0) {
>  				unsigned int plen = min(sglen, (unsigned int)
>  						PAGE_SIZE - poff);
> -				unsigned char *ptr = kmap(page);
>  
>  				if (dir == TO_XFER_BUF)
> -					memcpy(ptr + poff, buffer + cnt, plen);
> +					memcpy_to_page(page, poff, buffer + cnt, plen);
>  				else
> -					memcpy(buffer + cnt, ptr + poff, plen);
> -				kunmap(page);
> +					memcpy_from_page(buffer + cnt, page, poff, plen);

This code is great...  But I went and looked at the function and found a
comment which needs to be updated as well.  :-/

 57         /*
 58          * Using scatter-gather.  We have to go through the list one entry
 59          * at a time.  Each s-g entry contains some number of pages, and
 60          * each page has to be kmap()'ed separately.
 61          */

I would update it to say something like:

...  Each s-g entry contains some number of pages which have to be copied one
at a time.

Sorry for not catching that earlier,
Ira

>  
>  				/* Start at the beginning of the next page */
>  				poff = 0;
> -- 
> 2.34.1
>