[PATCH v6 2/9] drm/xe: Add ASCII85 dump helper function

[John Harrison]

On 8/30/2024 10:29, John Harrison wrote:
> On 8/29/2024 23:23, John.C.Harrison at Intel.com wrote:
>> From: John Harrison <John.C.Harrison at Intel.com>
>>
>> There is a need to include the GuC log and other large binary objects
>> in core dumps and via dmesg. So add a helper for dumping to a printer
>> function via conversion to ASCII85 encoding.
>>
>> Another issue with dumping such a large buffer is that it can be slow,
>> especially if dumping to dmesg over a serial port. So add a yield to
>> prevent the 'task has been stuck for 120s' kernel hang check feature
>> from firing.
>>
>> Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> The intent would be to use this helper for the existing ascii85 dumps 
> in xe_lrc.c and xe_vm.c. Otherwise those will hit problems with 
> maximum line lengths when spewing a devcoredump to dmesg. However, 
> that will also add line wrapping to the regular devcoredump via sysfs 
> output. And I'm not sure if that would confuse the decoding tool? 
> White space should just be ignored when decoding ASCII85 but the tool 
> might well not be aware that the data spans multiple lines.
>
> One thought is to move the line wrapping out of the encoding helper 
> and in to the drm line printer helper. However that would require 
> putting memory allocation operations in the line printer and that 
> seems more problematic as that could be used in atomic context. It 
> seems much simpler/safer to just allow for line wrapping in the sysfs 
> output.

PS: Meant to add that using the helper in the LRC/VM code would also 
allow those to benefit from compression when I get around to adding that 
in. And that will significantly shrink the devcoredump file size. 
Especially when dumping large user buffers!

John.

>
> John.
>
>> ---
>>   drivers/gpu/drm/xe/xe_devcoredump.c | 76 +++++++++++++++++++++++++++++
>>   drivers/gpu/drm/xe/xe_devcoredump.h |  5 ++
>>   2 files changed, 81 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_devcoredump.c 
>> b/drivers/gpu/drm/xe/xe_devcoredump.c
>> index bdb76e834e4c..eec7b89ab48b 100644
>> --- a/drivers/gpu/drm/xe/xe_devcoredump.c
>> +++ b/drivers/gpu/drm/xe/xe_devcoredump.c
>> @@ -6,6 +6,7 @@
>>   #include "xe_devcoredump.h"
>>   #include "xe_devcoredump_types.h"
>>   +#include <linux/ascii85.h>
>>   #include <linux/devcoredump.h>
>>   #include <generated/utsrelease.h>
>>   @@ -310,3 +311,78 @@ int xe_devcoredump_init(struct xe_device *xe)
>>   }
>>     #endif
>> +
>> +/**
>> + * xe_print_blob_ascii85 - print a BLOB to some useful location in 
>> ASCII85
>> + *
>> + * The output is split to multiple lines because some print targets, 
>> e.g. dmesg
>> + * cannot handle arbitrarily long lines. Note also that printing to 
>> dmesg in
>> + * piece-meal fashion is not possible, each separate call to 
>> drm_puts() has a
>> + * line-feed automatically added! Therefore, the entire output line 
>> must be
>> + * constructed in a local buffer first, then printed in one atomic 
>> output call.
>> + *
>> + * There is also a scheduler yield call to prevent the 'task has 
>> been stuck for
>> + * 120s' kernel hang check feature from firing when printing to a 
>> slow target
>> + * such as dmesg over a serial port.
>> + *
>> + * TODO: Add compression prior to the ASCII85 encoding to shrink 
>> huge buffers down.
>> + *
>> + * @p: the printer object to output to
>> + * @blob: the Binary Large OBject to dump out
>> + * @offset: offset in bytes to skip from the front of the BLOB, must 
>> be a multiple of sizeof(u32)
>> + * @size: the size in bytes of the BLOB, must be a multiple of 
>> sizeof(u32)
>> + */
>> +void xe_print_blob_ascii85(struct drm_printer *p, const void *blob, 
>> size_t offset, size_t size)
>> +{
>> +    const u32 *blob32 = (const u32 *)blob;
>> +    char buff[ASCII85_BUFSZ], *line_buff;
>> +    size_t line_pos = 0;
>> +
>> +#define DMESG_MAX_LINE_LEN    800
>> +#define MIN_SPACE        (ASCII85_BUFSZ + 2)        /* 85 + "\n\0" */
>> +
>> +    if (size & 3)
>> +        drm_printf(p, "Size not word aligned: %zu", size);
>> +    if (offset & 3)
>> +        drm_printf(p, "Offset not word aligned: %zu", size);
>> +
>> +    line_buff = kzalloc(sizeof(DMESG_MAX_LINE_LEN), GFP_KERNEL);
>> +    if (IS_ERR(line_buff)) {
>> +        drm_printf(p, "Failed to allocate line buffer: %pe", 
>> line_buff);
>> +        return;
>> +    }
>> +
>> +    blob32 += offset / sizeof(*blob32);
>> +    size /= sizeof(*blob32);
>> +
>> +    while (size--) {
>> +        u32 val = *(blob32++);
>> +
>> +        strscpy(line_buff + line_pos, ascii85_encode(val, buff),
>> +            DMESG_MAX_LINE_LEN - line_pos);
>> +        line_pos += strlen(line_buff + line_pos);
>> +
>> +        if ((line_pos + MIN_SPACE) >= DMESG_MAX_LINE_LEN) {
>> +            line_buff[line_pos++] = '\n';
>> +            line_buff[line_pos++] = 0;
>> +
>> +            drm_puts(p, line_buff);
>> +
>> +            line_pos = 0;
>> +
>> +            /* Prevent 'stuck thread' time out errors */
>> +            cond_resched();
>> +        }
>> +    }
>> +
>> +    if (line_pos) {
>> +        line_buff[line_pos++] = '\n';
>> +        line_buff[line_pos++] = 0;
>> +
>> +        drm_puts(p, line_buff);
>> +    }
>> +
>> +    kfree(line_buff);
>> +
>> +#undef MIN_SPACE
>> +}
>> diff --git a/drivers/gpu/drm/xe/xe_devcoredump.h 
>> b/drivers/gpu/drm/xe/xe_devcoredump.h
>> index e2fa65ce0932..3f82188590ac 100644
>> --- a/drivers/gpu/drm/xe/xe_devcoredump.h
>> +++ b/drivers/gpu/drm/xe/xe_devcoredump.h
>> @@ -6,6 +6,9 @@
>>   #ifndef _XE_DEVCOREDUMP_H_
>>   #define _XE_DEVCOREDUMP_H_
>>   +#include <linux/types.h>
>> +
>> +struct drm_printer;
>>   struct xe_device;
>>   struct xe_sched_job;
>>   @@ -23,4 +26,6 @@ static inline int xe_devcoredump_init(struct 
>> xe_device *xe)
>>   }
>>   #endif
>>   +void xe_print_blob_ascii85(struct drm_printer *p, const void 
>> *blob, size_t offset, size_t size);
>> +
>>   #endif
>